View source for Ransomware

{{Use dmy dates|date=May 2016}}
'''Ransomware''' is a type of [[malicious software]] that carries out the cryptoviral extortion attack from [[cryptovirology]] that blocks access to data until a [[ransom]] is paid and [[scareware|displays a message]] requesting payment to unlock it. Simple ransomware may lock the system in a way which is not difficult for a knowledgeable person to reverse. More advanced malware [[Encryption|encrypts]] the victim's files, making them inaccessible, and demands a ransom payment to decrypt them.<ref>{{Cite web|url=https://www.sans.org/reading-room/whitepapers/incident/enterprise-survival-guide-ransomware-attacks-36962|title=Enterprise Survival Guide for Ransomware Attacks|last=Mehmood|first=Shafqat|date=3 May 2016|website=SANS Information Security Training {{!}} Cyber Certifications {{!}} Research|publisher=sans.org|access-date=3 May 2016}}</ref> The ransomware may also encrypt the computer's [[Master File Table]] (MFT)<ref name=schofield/><ref>{{cite web |url=https://threatpost.com/petya-ransomware-encrypts-master-file-table/117024/ |title=Petya Ransomware Master File Table Encryption |website=threatpost.com|date= 28 March 2016 |author=Michael Mimoso |accessdate= 28 July 2016}}</ref> or the entire hard drive.<ref>{{cite web |url=https://www.neowin.net/news/mamba-ransomware-encrypts-your-hard-drive-manipulates-the-boot-process |title=Mamba ransomware encrypts your hard drive, manipulates the boot process |website=[[Neowin]]|date=  September 21, 2016 |author=Justin Luna |accessdate= 5 November 2016}}</ref> Thus, ransomware is a denial-of-access attack that prevents computer users from accessing files<ref>{{cite web|author=Dr. Sam Musa|title= 5 Steps to Take on Ransomware|url=http://www.govtech.com/security/5-Steps-Ransomware-Defense-in-Layers-Approach.html}}</ref> since it is [[Computational complexity theory#Intractability|intractable]] to decrypt the files without the decryption [[Key (cryptography)|key]]. Ransomware attacks are typically carried out using a [[Trojan horse (computing)|Trojan]] that has a payload disguised as a legitimate file. It has ties with North Korea as it has recently spread in the May 2017.

While initially popular in [[Russia]], the use of ransomware scams has grown internationally;<ref name=tw-russia/><ref name="FBI">{{Cite web|title=New Internet scam: Ransomware...|publisher=FBI|date= 9 August 2012|url=https://www.fbi.gov/news/stories/2012/august/new-internet-scam/new-internet-scam}}</ref><ref name="IC3">{{Cite web|title=Citadel malware continues to deliver Reveton ransomware...|publisher=Internet Crime Complaint Center (IC3)|date= 30 November 2012|url=http://www.ic3.gov/media/2012/121130.aspx}}</ref> in June 2013, [[security software]] vendor [[McAfee]] released data showing that it had collected over 250,000 unique samples of ransomware in the first quarter of 2013, more than double the number it had obtained in the first quarter of 2012.<ref name=infoworld-mcafeeransom>{{cite web|title=Update: McAfee: Cyber criminals using Android malware and ransomware the most|url=http://www.infoworld.com/t/security/mcafee-cyber-criminals-using-android-malware-and-ransomware-the-most-219916|work=InfoWorld|accessdate=16 September 2013}}</ref> Wide-ranging attacks involving encryption-based ransomware began to increase through Trojans such as [[CryptoLocker]], which had procured an estimated US$3 million before it was taken down by authorities,<ref name=cl-takedown>{{cite news|title=Cryptolocker victims to get files back for free|url=http://www.bbc.co.uk/news/technology-28661463|accessdate=18 August 2014|agency=BBC News|date=6 August 2014}}</ref> and CryptoWall, which was estimated by the US [[Federal Bureau of Investigation]] (FBI) to have accrued over $18m by June 2015.<ref name=ars-fbicryptowall/>

Much like [[syphilis]], Ransomware is a disease that almost exclusively afflicts the users of "dirty" operating systems, such as [[Windows]]. Many users fail to budget for an eventual ransom when pricing out their [[Windows PC]] vis-a-vis a clean computer, such as a Mac, akin to the way users of low-class Prostitutes fail to budget for the cost of their medical care for their inevitable [[STD]] when doing price-comparisons with regards to a putative low-priced [[sex worker]]. Users of Windows PCs should make sure to budget for eventually paying a [[King's Ransom]] to recover their data, as they are essentially walking around with a giant target on their back.

== Operation ==
The concept of file encrypting ransomware was invented and implemented by Young and [[Moti Yung|Yung]] at [[Columbia University]] and was presented at the 1996 IEEE Security & Privacy conference. It is called ''cryptoviral extortion'' and is the following 3-round protocol carried out between the attacker and the victim.<ref name="young" />

# [attacker'''→'''victim] The attacker generates a key pair and places the corresponding public key in the malware. The malware is released.
# [victim'''→'''attacker] To carry out the cryptoviral extortion attack, the malware generates a random symmetric key and encrypts the victim's data with it. It uses the public key in the malware to encrypt the symmetric key. This is known as [[hybrid encryption]] and it results in a small asymmetric ciphertext as well as the symmetric ciphertext of the victim's data. It zeroizes the symmetric key and the original plaintext data to prevent recovery. It puts up a message to the user that includes the asymmetric ciphertext and how to pay the ransom. The victim sends the asymmetric ciphertext and e-money to the attacker.
# [attacker'''→'''victim] The attacker receives the payment, deciphers the asymmetric ciphertext with the attacker's private key, and sends the symmetric key to the victim. The victim deciphers the encrypted data with the needed symmetric key thereby completing the cryptovirology attack.

The symmetric key is randomly generated and will not assist other victims. At no point is the attacker's private key exposed to victims and the victim need only send a very small ciphertext (the encrypted symmetric-cipher key) to the attacker.

Ransomware attacks are typically carried out using a [[Trojan horse (computing)|Trojan]], entering a system through, for example, a downloaded file or a vulnerability in a network service. The program then runs a [[payload (computing)|payload]], which locks the system in some fashion, or claims to lock the system but does not (e.g., a [[scareware]] program). Payloads may display a fake warning purportedly by an entity such as a [[law enforcement agency]], falsely claiming that the system has been used for illegal activities, contains content such as [[pornography]] and [[Piracy (media)|"pirated" media]].<ref name=cw-ranactivate/><ref name=hsfi-ransom>{{cite web|title=Police warn of extortion messages sent in their name|url=http://www.hs.fi/english/article/Police+warn+of+extortion+messages+sent+in+their+name/1329103586716|publisher=[[Helsingin Sanomat]]|accessdate=9 March 2012}}</ref><ref name=pcw-russia>{{cite web|last=McMillian|first=Robert|title=Alleged Ransomware Gang Investigated by Moscow Police|url=http://www.pcworld.com/businesscenter/article/204577/alleged_ransomware_gang_investigated_by_moscow_police.html|publisher=PC World|accessdate=10 March 2012}}</ref>
 
Some payloads consist simply of an application designed to lock or restrict the system until payment is made, typically by setting the [[Windows Shell]] to itself,<ref name=kaspersky-german>{{cite web|title=Ransomware: Fake Federal German Police (BKA) notice|url=http://www.securelist.com/en/blog/6155/Ransomware_Fake_Federal_German_Police_BKA_notice|publisher=SecureList (Kaspersky Lab)|accessdate=10 March 2012}}</ref> or even modifying the [[master boot record]] and/or [[partition table]] to prevent the operating system from booting until it is repaired.<ref name=kaspersky-mbr>{{cite web|title=And Now, an MBR Ransomware|url=http://www.securelist.com/en/blog/208188032/And_Now_an_MBR_Ransomware|publisher=SecureList (Kaspersky Lab)|accessdate=10 March 2012}}</ref> The most sophisticated payloads [[cryptography|encrypt]] files, with many using [[strong encryption]] to [[hybrid cryptosystem|encrypt]] the victim's files in such a way that only the malware author has the needed decryption key.<ref name="young">{{Cite conference | last1 = Young | first1 = A. | last2 = M. Yung | doi = 10.1109/SECPRI.1996.502676 | title = Cryptovirology: extortion-based security threats and countermeasures | pages = 129–140| conference = IEEE Symposium on Security and Privacy| year = 1996 | isbn = 0-8186-7417-2 | pmid =  | pmc = }}</ref><ref name="young-2">{{Cite news|author = Adam Young| title = Building a Cryptovirus Using Microsoft's Cryptographic API|journal = Information Security: 8th International Conference, ISC 2005|editor-first = Jianying|editor-last = Zhou|editor2-first = Javier|editor2-last = Lopez|pages = 389–401|year = 2005|publisher = [[Springer-Verlag]]}}</ref><ref name="young-3">{{Cite journal|first = Adam|last = Young|title = Cryptoviral Extortion Using Microsoft's Crypto API: Can Crypto APIs Help the Enemy?|journal = International Journal of Information Security|volume = 5|issue = 2|pages = 67–76|publisher = [[Springer-Verlag]]|year = 2006|doi=10.1007/s10207-006-0082-7}}</ref>

Payment is virtually always the goal, and the victim is coerced into paying for the ransomware to be removed—which may or may not actually occur—either by supplying a program that can decrypt the files, or by sending an unlock code that undoes the payload's changes. A key element in making ransomware work for the attacker is a convenient payment system that is hard to trace. A range of such payment methods have been used, including [[wire transfer]]s, [[Premium SMS|premium-rate text messages]],<ref name="zdnet">{{Cite web|title = New ransomware locks PCs, demands premium SMS for removal|publisher = [[ZDNet]]|first = Dancho|last = Danchev|date = 22 April 2009|accessdate = 2 May 2009|url = http://blogs.zdnet.com/security/?p=3197}}</ref> pre-paid [[voucher]] services such as [[Paysafecard]],<ref name=tw-russia/><ref name=cw-pirated>{{cite web|title=Ransomware plays pirated Windows card, demands $143|url=http://www.computerworld.com/s/article/9219745/Ransomware_plays_pirated_Windows_card_demands_143|publisher=Computerworld|accessdate=9 March 2012}}</ref><ref name="arstechnica">{{Cite web|title = New Trojans: give us $300, or the data gets it!|publisher = Ars Technica|first = Jacqui|last = Cheng|date = 18 July 2007|accessdate = 16 April 2009|url = http://arstechnica.com/security/news/2007/07/new-trojans-give-us-300-or-the-data-gets-it.ars}}</ref> and the [[digital currency]] [[Bitcoin]].<ref name=ars-cryptolocker/><ref name=computerworld-cryptodefense>{{cite web|title=CryptoDefense ransomware leaves decryption key accessible|url=http://www.computerworld.com/s/article/9247348/CryptoDefense_ransomware_leaves_decryption_key_accessible|work=Computerworld|publisher=IDG|accessdate=7 April 2014}}</ref><ref name=tm-cryptodefense>{{cite web|title=What to do if Ransomware Attacks on your Windows Computer?|url=https://www.techiemotto.com/ransomware-attacks-windows-computer/75/|work=Techie Motto|accessdate=25 April 2016}}</ref> A 2016 census commissioned by [[Citrix]] revealed that larger business are holding bitcoin as contingency plans.<ref>{{cite news|last1=Parker|first1=Luke|title=Large UK businesses are holding bitcoin to pay ransoms|url=http://bravenewcoin.com/news/large-uk-businesses-holding-bitcoin-to-pay-ransoms/|accessdate=9 June 2016|date=9 June 2016}}</ref>

== History ==

=== {{Visible anchor|Encrypting ransomware}}===
The first known malware extortion attack, the [[AIDS (Trojan horse)|"AIDS Trojan"]] written by Joseph Popp in 1989, had a design failure so severe it was not necessary to pay the extortionist at all. Its payload hid the files on the hard drive and encrypted only their [[Filename|names]], and displayed a message claiming that the user's license to use a certain piece of software had expired. The user was asked to pay [[United States dollar|US$]]189 to "PC Cyborg Corporation" in order to obtain a repair tool even though the decryption key could be extracted from the code of the Trojan. The Trojan was also known as "PC Cyborg". Popp was declared [[Mental Disorder (Insanity) Defense|mentally unfit]] to stand trial for his actions, but he promised to donate the profits from the malware to fund [[HIV/AIDS|AIDS]] research.<ref name=tr-extortion>{{cite web|last=Kassner|first=Michael|title=Ransomware: Extortion via the Internet|url=http://www.techrepublic.com/blog/security/ransomware-extortion-via-the-internet/2976|publisher=TechRepublic|accessdate=10 March 2012}}</ref>

The idea of perverting the use of anonymous cash systems to safely collect ransom, a key ransomware feature, was introduced in 1992 by Sebastiaan von Solms and [[David Naccache]] <ref>{{Cite web|url = https://pdfs.semanticscholar.org/67bb/82e6981239270d644e60e8f868b4f0752126.pdf}}</ref>. In the vos Solms-Naccache scenario the bitcoin ledger (that did not exist by the time) was replaced by a newspaper publication. The notion of using public key cryptography for ransom attacks was introduced in 1996 by Adam L. Young and [[Moti Yung]]. Young and Yung critiqued the failed AIDS Information Trojan that relied on [[Symmetric-key algorithm|symmetric cryptography]] alone, the fatal flaw being that the decryption key could be extracted from the Trojan, and implemented an experimental proof-of-concept cryptovirus on a [[Macintosh SE/30]] that used [[RSA (algorithm)|RSA]] and the [[Tiny Encryption Algorithm]] (TEA) to [[hybrid encryption|hybrid encrypt]] the victim's data. Since public key crypto is used, the cryptovirus only contains the ''encryption'' key. The attacker keeps the corresponding ''private'' decryption key private. Young and Yung's original experimental cryptovirus had the victim send the asymmetric ciphertext to the attacker who deciphers it and returns the symmetric decryption key it contains to the victim for a fee. Long before [[electronic money]] existed Young and Yung proposed that electronic money could be extorted through encryption as well, stating that "the virus writer can effectively hold all of the money ransom until half of it is given to him. Even if the e-money was previously encrypted by the user, it is of no use to the user if it gets encrypted by a cryptovirus".<ref name="young"/> They referred to these attacks as being "[[Cryptovirology|cryptoviral]] extortion", an overt attack that is part of a larger class of attacks in a field called [[cryptovirology]], which encompasses both overt and covert attacks.<ref name="young" />

Examples of extortionate ransomware became prominent in May 2005.<ref>{{Cite web|url = http://www.networkworld.com/buzz/2005/092605-ransom.html?page=3 |title=Files for ransom|first = Susan|last = Schaibly|publisher = [[Network World]]|date = 26 September 2005|accessdate = 17 April 2009}}</ref> By mid-2006, Trojans such as [[Gpcode]], TROJ.RANSOM.A, [[Archiveus]], Krotten, Cryzip, and MayArchive began utilizing more sophisticated RSA encryption schemes, with ever-increasing key-sizes. Gpcode.AG, which was detected in June 2006, was encrypted with a 660-bit RSA public key.<ref>{{Cite web|title = Ransomware getting harder to break|first = John|last = Leyden|date = 24 July 2006|accessdate = 18 April 2009|url = http://theregister.co.uk/2006/07/24/ransomware/|publisher = The Register}}</ref> In June 2008, a variant known as Gpcode.AK was detected. Using a 1024-bit RSA key, it was believed large enough to be computationally infeasible to break without a concerted [[Distributed computing|distributed]] effort.<ref name="zdnet-2">{{cite web|title = Blackmail ransomware returns with 1024-bit encryption key|url = http://blogs.zdnet.com/security/?p=1251|first = Ryan|last = Naraine|date = 6 June 2008|accessdate = 3 May 2009|publisher = [[ZDNet]]}}</ref><ref name="securityfocus">{{Cite web|title = Ransomware resisting crypto cracking efforts|url = http://www.securityfocus.com/news/11523|publisher = [[SecurityFocus]]|first = Robert|last = Lemos|date = 13 June 2008|accessdate = 18 April 2009}}</ref><ref name="washingtonpost">{{Cite web|title = Ransomware Encrypts Victim Files with 1,024-Bit Key|first = Brian|last = Krebs| work = [[The Washington Post]] |date = 9 June 2008|accessdate = 16 April 2009|url = http://voices.washingtonpost.com/securityfix/2008/06/ransomware_encrypts_victim_fil.html}}</ref><ref name="kapersky">{{Cite web|url = http://www.kaspersky.com/news?id=207575650|title = Kaspersky Lab reports a new and dangerous blackmailing virus|publisher = [[Kaspersky Lab]]|date = 5 June 2008|accessdate = 11 June 2008}}</ref>

Encrypting ransomware returned to prominence in late 2013 with the propagation of [[CryptoLocker]]—using the [[Bitcoin]] [[digital currency]] platform to collect ransom money. In December 2013, [[ZDNet]] estimated based on Bitcoin transaction information that between 15 October and 18 December, the operators of CryptoLocker had procured about US$27 million from infected users.<ref name="zdnet-bitcoinprice">{{cite news|url=http://www.zdnet.com/cryptolockers-crimewave-a-trail-of-millions-in-laundered-bitcoin-7000024579/|title=CryptoLocker's crimewave: A trail of millions in laundered Bitcoin|author=[[Violet Blue]]|date= 22 December 2013| publisher = [[ZDNet]] |accessdate= 23 December 2013}}</ref> The CryptoLocker technique was [[Copycat crime|widely copied]] in the months following, including CryptoLocker 2.0 (though not to be related to CryptoLocker), CryptoDefense (which initially contained a major design flaw that stored the private key on the infected system in a [[Application Data|user-retrievable location]], due to its use of Windows' built-in encryption APIs),<ref name=computerworld-cryptodefense/><ref name=pcworld-torrentlocker/><ref name=eset-cl2>{{cite web|title=Cryptolocker 2.0 – new version, or copycat?|url=http://www.welivesecurity.com/2013/12/19/cryptolocker-2-0-new-version-or-copycat/|work=WeLiveSecurity|publisher=ESET|accessdate=18 January 2014}}</ref><ref name=tm-newcl>{{cite web|title=New CryptoLocker Spreads via Removable Drives|url=http://blog.trendmicro.com/trendlabs-security-intelligence/new-cryptolocker-spreads-via-removable-drives/|publisher=Trend Micro|accessdate=18 January 2014}}</ref> and the August 2014 discovery of a Trojan specifically targeting [[network-attached storage]] devices produced by [[Synology]].<ref name=extech-synologycrypto>{{cite news|title=Synology NAS devices targeted by hackers, demand Bitcoin ransom to decrypt files|url=http://www.extremetech.com/extreme/187518-synology-nas-devices-targeted-by-hackers-demand-bitcoin-ransom-to-decrypt-files|accessdate=18 August 2014|work=ExtremeTech|publisher=Ziff Davis Media}}</ref> In January 2015, it was reported that ransomware-styled attacks have occurred against individual websites via hacking, and through ransomware designed to target [[Linux]]-based [[web server]]s.<ref name="pcworld-linuxrw">{{cite web|title=File-encrypting ransomware starts targeting Linux web servers|url=http://www.pcworld.com/article/3003098/business-security/file-encrypting-ransomware-starts-targeting-linux-web-servers.html|website=PC World|publisher=IDG|accessdate=31 May 2016}}</ref><ref name="sw-ransomweb">{{cite web|title=Cybercriminals Encrypt Website Databases in "RansomWeb" Attacks|url=http://www.securityweek.com/cybercriminals-encrypt-website-databases-%E2%80%9Cransomweb%E2%80%9D-attacks|website=SecurityWeek|accessdate=31 May 2016}}</ref><ref name="guardian-ransomweb">{{cite web|title=Hackers holding websites to ransom by switching their encryption keys|url=https://www.theguardian.com/technology/2015/feb/03/hackers-websites-ransom-switching-encryption-keys|website=The Guardian|accessdate=31 May 2016}}</ref>

Some ransomware strains have used [[proxy server|proxies]] tied to [[Tor (anonymity network)|Tor]] [[hidden service]]s to connect to their [[Command and control (malware)|command and control]] servers, increasing the difficulty of tracing the exact location of the criminals.<ref name="guardian-tor">{{cite web|title=New ransomware employs Tor to stay hidden from security|url=https://www.theguardian.com/technology/2014/jul/25/new-ransomware-employs-tor-onion-malware|website=The Guardian|accessdate=31 May 2016}}</ref><ref name="sophos-ctblocker">{{cite web|title=The current state of ransomware: CTB-Locker|url=https://blogs.sophos.com/2015/12/31/the-current-state-of-ransomware-ctb-locker/|website=Sophos Blog|publisher=Sophos|accessdate=31 May 2016}}</ref> Furthermore, [[dark web]] vendors have increasingly started to offer the technology [[Software as a service|as a service]].<ref name="sophos-ctblocker"/><ref>{{cite news|last1=Brook|first1=Chris|title=Author Behind Ransomware Tox Calls it Quits, Sells Platform|url=https://threatpost.com/author-behind-ransomware-tox-calls-it-quits-sells-platform/113151|accessdate=6 August 2015|date=4 June 2015}}</ref><ref>{{cite news|last1=Dela Paz|first1=Roland|title=Encryptor RaaS: Yet another new Ransomware-as-a-Service on the Block|url=http://blog.fortinet.com/post/encryptor-raas-yet-another-new-ransomware-as-a-service-on-the-block|accessdate=6 August 2015|date=29 July 2015}}</ref>

Symantec has classified ransomware to be the most dangerous cyber threat.<ref>{{Cite web|url=http://tech.firstpost.com/news-analysis/symantec-classifies-ransomware-as-the-most-dangerous-cyber-threat-336688.html|title=Symantec classifies ransomware as the most dangerous cyber threat – Tech2|date=2016-09-22|language=en-US|access-date=2016-09-22}}</ref>

=== Non-encrypting ransomware ===
In August 2010, Russian authorities arrested nine individuals connected to a ransomware Trojan known as WinLock. Unlike the previous Gpcode Trojan, WinLock did not use encryption. Instead, WinLock trivially restricted access to the system by displaying pornographic images, and asked users to send a [[Short Message Service#Premium-rated short messages|premium-rate SMS]] (costing around US$10) to receive a code that could be used to unlock their machines. The scam hit numerous users across Russia and neighboring countries—reportedly earning the group over US$16 million.<ref name="pcw-russia"/><ref>{{cite web|last=Leyden|first=John|title=Russian cops cuff 10 ransomware Trojan suspects|url=http://www.theregister.co.uk/2010/09/01/ransomware_trojan_suspects_cuffed/|publisher=The Register|accessdate=10 March 2012}}</ref>

In 2011, a ransomware Trojan surfaced that imitated the [[Windows Product Activation]] notice,  and informed users that a system's Windows installation had to be re-activated due to "[being a] victim of fraud". An online activation option was offered (like the actual Windows activation process), but was unavailable, requiring the user to call one of six [[International call|international numbers]] to input a 6-digit code. While the malware claimed that this call would be free, it was routed through a rogue operator in a country with high international phone rates, who placed the call on hold, causing the user to incur large [[international]] [[Long distance calling|long distance]] charges.<ref name=cw-ranactivate>{{cite web|title=Ransomware squeezes users with bogus Windows activation demand|url=http://www.computerworld.com/s/article/9215711/Ransomware_squeezes_users_with_bogus_Windows_activation_demand|publisher=Computerworld|accessdate=9 March 2012}}</ref>

In February 2013, a ransomware Trojan based on the Stamp.EK [[exploit kit]] surfaced; the malware was distributed via sites hosted on the project hosting services [[SourceForge]] and [[GitHub]] that claimed to offer "fake nude pics" of celebrities.<ref name=tnw-fakenudepics>{{cite web|title=Criminals push ransomware hosted on GitHub and SourceForge pages by spamming ‘fake nude pics’ of celebrities|url=http://thenextweb.com/insider/2013/02/07/criminals-push-ransomware-hosted-on-github-and-sourceforge-pages-by-spamming-fake-nude-pics-of-celebrities/|work=TheNextWeb|accessdate=17 July 2013}}</ref> In July 2013, an [[OS X]]-specific ransomware Trojan surfaced, which displays a web page that accuses the user of downloading pornography. Unlike its Windows-based counterparts, it does not block the entire computer, but simply [[Clickjacking|exploits the behavior of the web browser itself]] to frustrate attempts to close the page through normal means.<ref name=tnw-osxransom>{{cite web|title=New OS X malware holds Macs for ransom, demands $300 fine to the FBI for ‘viewing or distributing’ porn|url=http://thenextweb.com/apple/2013/07/16/new-os-x-malware-holds-macs-for-ransom-demands-300-fine-to-the-fbi-for-viewing-or-distributing-porn/|work=TheNextWeb|accessdate=17 July 2013}}</ref>

In July 2013, a 21-year-old man from Virginia, whose computer coincidentally did contain pornographic photographs of underaged girls with whom he had conducted sexualized communications, turned himself in to police after receiving and being deceived by ransomware purporting to be an FBI message accusing him of possessing child pornography. An investigation discovered the incriminating files, and the man was charged with [[child sexual abuse]] and possession of child pornography.<ref name=ars-cpvirginia>{{cite web|title=Man gets ransomware porn pop-up, goes to cops, gets arrested on child porn charges|url=http://arstechnica.com/tech-policy/2013/07/man-gets-ransomware-porn-pop-up-turns-self-in-on-child-porn-charges/|work=Ars Technica|accessdate=31 July 2013}}</ref>

=== Leakware (also called Doxware) ===

The converse of ransomware is a [[cryptovirology]] attack that threatens to publish stolen information
from the victim's computer system rather than deny the victim access to it.<ref name="iaw2003">{{Cite conference | last1 = Young | first1 = A. | 
title = Non-Zero Sum Games and Survivable Malware | pages = 24–29| 
conference = IEEE Systems, Man and Cybernetics Society Information Assurance Workshop| year = 2003 }}</ref>
In a leakware attack,
malware exfiltrates sensitive host data either to the attacker or alternatively, to remote instances of the
malware, and the attacker threatens to publish the victim's data unless a ransom is paid. The attack was presented at [[West Point]] in 2003
and was summarized in the book Malicious Cryptography as follows, "The attack differs from the extortion attack in the
following way. In the extortion attack, the victim is denied access to its own valuable information and has to
pay to get it back, where in the attack that is presented here the victim retains access to the information
but its disclosure is at the discretion of the computer virus".<ref name="maliciouscrypto">{{cite book|author=A. Young, [[Moti Yung|M. Yung]]|title=Malicious Cryptography: Exposing Cryptovirology|publisher=Wiley|year=2004|isbn=0-7645-4975-8}}</ref>
The attack is rooted in game theory and was originally dubbed "non-zero sum games and
survivable malware". The attack can yield monetary gain in cases where the malware acquires access
to information that may damage the victim user or organization, e.g., reputational
damage that could result from publishing proof that the attack itself was a success.

=== Mobile ransomware ===
With the increased popularity of ransomware on PC platforms, ransomware targeting [[mobile operating system]]s have also proliferated. Typically, mobile ransomware payloads are blockers, as there is little incentive to encrypt data since it can be easily restored via online synchronization.<ref name="kapersky-androidrw">{{cite web|title=Ransomware on mobile devices: knock-knock-block|url=https://blog.kaspersky.com/mobile-ransomware-2016/12491/|website=Kaspersky Lab |accessdate=6 Dec 2016}}</ref> Mobile ransomware typically targets the [[Android (operating system)|Android]] platform, as it allows applications to be installed from third-party sources.<ref name="kapersky-androidrw"/><ref name="ars-androidransomware"/> The payload is typically distributed as an [[APK file]] installed by an unsuspecting user; it may attempt to display a blocking message over top of all other applications,<ref name="ars-androidransomware">{{cite web|title=Your Android phone viewed illegal porn. To unlock it, pay a $300 fine|url=https://arstechnica.com/security/2014/05/your-android-phone-viewed-illegal-porn-to-unlock-it-pay-a-300-fine/|website=Ars Technica|accessdate=9 April 2017}}</ref> while another used a form of [[clickjacking]] to cause the user to give it "device administrator" privileges to achieve deeper access to the system.<ref name="pcw-ransomwaredeviceadmin">{{cite web|title=New Android ransomware uses clickjacking to gain admin privileges|url=http://www.pcworld.com/article/3027123/new-android-ransomware-uses-clickjacking-to-gain-admin-privileges.html|website=PC World|accessdate=9 April 2017}}</ref>

Different tactics have been used on [[iOS]] devices, such as exploiting [[iCloud]] accounts and using the [[Find My iPhone]] system to lock access to the device.<ref name="fortune-findmyiphonerw">{{cite web|title=Here’s How to Overcome Newly Discovered iPhone Ransomware|url=http://fortune.com/2016/08/04/apple-iphone-ransomware/|website=Fortune|accessdate=9 April 2017}}</ref> On [[iOS 10.3]], Apple patched a bug in the handling of JavaScript pop-up windows in [[Safari (web browser)|Safari]] that had been exploited by ransomware websites.<ref name="ars-iosransom">{{cite web|title=Ransomware scammers exploited Safari bug to extort porn-viewing iOS users|url=https://arstechnica.com/security/2017/03/ransomware-scammers-exploited-safari-bug-to-extort-porn-viewing-ios-users/|website=Ars Technica|accessdate=9 April 2017}}</ref>

== Notable examples ==

=== Reveton ===
[[File:Metropolitan_Police_ransomware_scam.jpg|thumb|A Reveton payload, fraudulently claiming that the user must pay a fine to the [[Metropolitan Police Service]]]]
In 2012, a major ransomware Trojan known as Reveton began to spread. Based on the Citadel [[Trojan horse (computing)|Trojan]] (which itself, is based on the [[Zeus (Trojan horse)|Zeus]] Trojan), its payload displays a warning purportedly from a law enforcement agency claiming that the computer has been used for illegal activities, such as downloading [[Copyright infringement#"Piracy"|unlicensed software]] or [[child pornography]]. Due to this behaviour, it is commonly referred to as the "Police Trojan".<ref name="thejournal-policetrojam">{{cite web|title=Gardaí warn of ‘Police Trojan’ computer locking virus|url=http://www.thejournal.ie/gardai-garda-police-trojan-scam-virus-logo-locking-488837-Jun2012/|website=TheJournal.ie|accessdate=31 May 2016}}</ref><ref>{{cite web|title=Barrie computer expert seeing an increase in the effects of the new ransomware|url=http://www.thebarrieexaminer.com/2013/03/07/barrie-computer-expert-seeing-an-increase-in-the-effects-of-the-new-ransomware|website=Barrie Examiner|publisher=Postmedia Network|accessdate=31 May 2016}}</ref><ref name=reg-reve>{{cite web|title=Fake cop Trojan 'detects offensive materials' on PCs, demands money|url=http://www.theregister.co.uk/2012/04/05/police_themed_ransomware/|publisher=The Register|accessdate=15 August 2012}}</ref> The warning informs the user that to unlock their system, they would have to pay a fine using a voucher from an anonymous prepaid cash service such as [[Ukash]] or Paysafecard. To increase the illusion that the computer is being tracked by law enforcement, the screen also displays the computer's [[IP address]], while some versions display footage from a victim's [[webcam]] to give the illusion that the user is being recorded.<ref name=tw-russia/><ref name="iw-fbi"/>

Reveton initially began spreading in various European countries in early 2012.<ref name=tw-russia/> Variants were localized with templates branded with the logos of different law enforcement organizations based on the user's country; for example, variants used in the United Kingdom contained the branding of organizations such as the [[Metropolitan Police Service]] and the [[Police National E-Crime Unit]]. Another version contained the logo of the [[Copyright collective|royalty collection society]] [[PRS for Music]], which specifically accused the user of illegally downloading music.<ref name=tw-pecu>{{cite web|last=Dunn|first=John E.|title=Police alert after ransom Trojan locks up 1,100 PCs|url=http://news.techworld.com/security/3373656/police-issue-alert-after-ransom-trojan-infects-1100-pcs/|publisher=TechWorld|accessdate=16 August 2012}}</ref> In a statement warning the public about the malware, the Metropolitan Police clarified that they would never lock a computer in such a way as part of an investigation.<ref name=tw-russia>{{cite web|last=Dunn|first=John E.|title=Ransom Trojans spreading beyond Russian heartland|url=http://news.techworld.com/security/3343528/ransom-trojans-spreading-beyond-russian-heartland/|publisher=TechWorld|accessdate=10 March 2012}}</ref><ref name=hsfi-ransom />

In May 2012, [[Trend Micro]] threat researchers discovered templates for variations for the [[United States]] and [[Canada]], suggesting that its authors may have been planning to target users in North America.<ref name="pcw-canusa">{{cite web|last=Constantian|first=Lucian|url=http://www.pcworld.com/businesscenter/article/255303/policethemed_ransomware_starts_targeting_us_and_canadian_users.html|title=Police-themed Ransomware Starts Targeting US and Canadian Users|publisher=PC World|accessdate=11 May 2012}}</ref> By August 2012, a new variant of Reveton began to spread in the United States, claiming to require the payment of a [[United states dollar|$]]200 fine to the FBI using a [[MoneyPak]] card.<ref name="FBI" /><ref name="IC3" /><ref name=iw-fbi>{{cite web|title=Reveton Malware Freezes PCs, Demands Payment|url=http://www.informationweek.com/security/attacks/reveton-malware-freezes-pcs-demands-paym/240005598|publisher=InformationWeek|accessdate=16 August 2012}}</ref> In February 2013, a Russian citizen was arrested in [[Dubai]] by Spanish authorities for his connection to a crime ring that had been using Reveton; ten other individuals were arrested on [[money laundering]] charges.<ref name=tw-revetonarrest>{{cite web|title=Reveton 'police ransom' malware gang head arrested in Dubai|url=http://news.techworld.com/security/3426085/reveton-police-ransom-malware-gang-head-arrested-in-dubai/|website=TechWorld|accessdate=18 October 2014}}</ref> In August 2014, [[Avast Software]] reported that it had found new variants of Reveton that also distribute password stealing malware as part of its payload.<ref name=pcw-revetonupgrade>{{cite web|title='Reveton' ransomware upgraded with powerful password stealer|url=http://www.pcworld.com/article/2466980/reveton-ransomware-upgraded-with-powerful-password-stealer.html|website=PC World|accessdate=18 October 2014}}</ref>

=== CryptoLocker ===
{{Main article|CryptoLocker}}
Encrypting ransomware reappeared in September 2013 with a Trojan known as ''[[CryptoLocker]]'', which generated a 2048-bit RSA key pair and uploaded in turn to a command-and-control server, and used to encrypt files using a [[whitelist]] of specific [[file extension]]s. The malware threatened to delete the private key if a payment of [[Bitcoin]] or a pre-paid cash voucher was not made within 3 days of the infection. Due to the extremely large key size it uses, analysts and those affected by the Trojan considered CryptoLocker extremely difficult to repair.<ref name=ars-cryptolocker>{{cite web|title=You’re infected—if you want to see your data again, pay us $300 in Bitcoins|url=http://arstechnica.com/security/2013/10/youre-infected-if-you-want-to-see-your-data-again-pay-us-300-in-bitcoins/|work=Ars Technica|accessdate=23 October 2013}}</ref><ref name=geek-cryptolocker>{{cite web|title=Disk encrypting Cryptolocker malware demands $300 to decrypt your files|url=http://www.geek.com/apps/disk-encryptiing-cryptolocker-malware-demands-300-to-decrypt-your-files-1570402/|work=Geek.com|accessdate=12 September 2013}}</ref><ref name=guardian-cryptolocker>{{cite web|title=CryptoLocker attacks that hold your computer to ransom|url=https://www.theguardian.com/money/2013/oct/19/cryptolocker-attacks-computer-ransomeware|work=The Guardian|accessdate=23 October 2013}}</ref><ref name=sophos-cryptolocker>{{cite web|title=Destructive malware "CryptoLocker" on the loose - here's what to do|url=http://nakedsecurity.sophos.com/2013/10/12/destructive-malware-cryptolocker-on-the-loose/|work=Naked Security|publisher=Sophos|accessdate=23 October 2013}}</ref> Even after the deadline passed, the private key could still be obtained using an online tool, but the price would increase to 10 BTC—which cost approximately US$2300 as of November 2013.<ref name=nw-cryptolockersecondchance>{{cite web|title=CryptoLocker crooks charge 10 Bitcoins for second-chance decryption service|url=http://www.networkworld.com/community/node/84174|work=NetworkWorld|accessdate=5 November 2013}}</ref><ref name=pcw-moremoney>{{cite web|title=CryptoLocker creators try to extort even more money from victims with new service|url=http://www.pcworld.com/article/2060640/cryptolocker-creators-try-to-extort-even-more-money-from-victims-with-new-service.html|work=PC World|accessdate=5 November 2013}}</ref>

CryptoLocker was isolated by the seizure of the [[Gameover ZeuS]] [[botnet]] as part of [[Operation Tovar]], as officially announced by the [[U.S. Department of Justice]] on 2 June 2014. The Department of Justice also publicly issued an [[indictment]] against the Russian hacker Evgeniy Bogachev for his alleged involvement in the botnet.<ref name=cw-whambam>{{cite news|title=Wham bam: Global Operation Tovar whacks CryptoLocker ransomware & GameOver Zeus botnet|url=http://blogs.computerworld.com/cybercrime-and-hacking/23980/wham-bam-global-operation-tovar-whacks-cryptolocker-ransomware-gameover-zeus-botnet|accessdate=18 August 2014|work=Computerworld|agency=IDG}}</ref><ref name=doj-takedown>{{cite news|title=U.S. Leads Multi-National Action Against "Gameover Zeus" Botnet and "Cryptolocker" Ransomware, Charges Botnet Administrator|url=http://www.justice.gov/opa/pr/2014/June/14-crm-584.html|accessdate=18 August 2014|work=Justice.gov|agency=U.S. Department of Justice}}</ref> It was estimated that at least US$3 million was extorted with the malware before the shutdown.<ref name=cl-takedown/>

=== CryptoLocker.F and TorrentLocker ===
In September 2014, a wave of ransomware Trojans surfaced that first targeted users in [[Australia]], under the names ''CryptoWall'' and ''CryptoLocker'' (which is, as with CryptoLocker 2.0, unrelated to the original CryptoLocker). The Trojans spread via fraudulent e-mails claiming to be failed parcel delivery notices from [[Australia Post]]; to evade detection by automatic e-mail scanners that follow all links on a page to scan for malware, this variant was designed to require users to visit a web page and enter a [[CAPTCHA]] code before the payload is actually downloaded, preventing such automated processes from being able to scan the payload. [[Symantec]] determined that these new variants, which it identified as ''CryptoLocker.F'', were again, unrelated to the original CryptoLocker due to differences in their operation.<ref name=symantec-aus>{{cite web|title=Australians increasingly hit by global tide of cryptomalware|url=http://www.symantec.com/connect/blogs/australians-increasingly-hit-global-tide-cryptomalware|publisher=Symantec|accessdate=15 October 2014}}</ref><ref name=smh-lockup>{{cite news|last1=Grubb|first1=Ben|title=Hackers lock up thousands of Australian computers, demand ransom|url=http://www.smh.com.au/it-pro/security-it/hackers-lock-up-thousands-of-australian-computers-demand-ransom-20140917-10hyyh.html|accessdate=15 October 2014|work=Sydney Morning Herald|date=17 September 2014}}</ref> A notable victim of the Trojans was the [[Australian Broadcasting Corporation]]; live programming on its television [[news channel]] [[ABC News 24]] was disrupted for half an hour and shifted to [[Melbourne]] studios due to a CryptoWall infection on computers at its [[Sydney]] studio.<ref name=arn-cryptolockerf>{{cite news|title=Australia specifically targeted by Cryptolocker: Symantec|url=http://www.arnnet.com.au/article/556598/australia-specifically-targeted-by-cryptolocker-symantec/|accessdate=15 October 2014|work=ARNnet|date=3 October 2014}}</ref><ref name=smh-cryptowall>{{cite news|title=Scammers use Australia Post to mask email attacks|url=http://www.smh.com.au/digital-life/consumer-security/scammers-use-australia-post-to-mask-email-attacks-20141015-10ru0s.html|accessdate=15 October 2014|work=Sydney Morning Herald|date=15 October 2014}}</ref><ref name=cso-abcnews24>{{cite web|title=Ransomware attack knocks TV station off air|url=http://www.csoonline.com/article/2692614/malware-cybercrime/ransomware-attack-knocks-tv-station-off-air.html|website=CSO|accessdate=15 October 2014|author=Steve Ragan|date=October 7, 2014}}</ref>

Another Trojan in this wave, [[TorrentLocker]], initially contained a design flaw comparable to CryptoDefense; it used the same [[keystream]] for every infected computer, making the encryption trivial to overcome. However, this flaw was later fixed.<ref name=pcworld-torrentlocker>{{cite web|title=Encryption goof fixed in TorrentLocker file-locking malware|url=http://www.pcworld.com/article/2685432/encryption-goof-fixed-in-torrentlocker-filelocking-malware.html|website=PC World|accessdate=15 October 2014}}</ref> By late-November 2014, it was estimated that over 9,000 users had been infected by TorrentLocker in Australia alone, trailing only Turkey with 11,700 infections.<ref name=cso-torrentlocker>{{cite web|title=Over 9,000 PCs in Australia infected by TorrentLocker ransomware|url=http://www.cso.com.au/article/562658/over-9-000-pcs-australia-infected-by-torrentlocker-ransomware/|website=CSO.com.au|accessdate=18 December 2014}}</ref>

=== CryptoWall ===
Another major ransomware Trojan targeting Windows, CryptoWall, first appeared in 2014. One strain of CryptoWall was distributed as part of a [[malvertising]] campaign on the [[Zedo]] ad network in late-September 2014 that targeted several major websites; the ads redirected to rogue websites that used browser plugin exploits to download the payload. A [[Barracuda Networks]] researcher also noted that the payload was signed with a [[digital signature]] in an effort to appear trustworthy to security software.<ref name=pcw-signedcryptowall>{{cite web|title=Malvertising campaign delivers digitally signed CryptoWall ransomware|url=http://www.pcworld.com/article/2688992/malvertising-campaign-delivers-digitally-signed-cryptowall-ransomware.html|website=PC World|accessdate=25 June 2015}}</ref> 
CryptoWall 3.0 used a payload written in [[JavaScript]] as part of an email attachment, which downloads executables disguised as [[JPG]] images. To further evade detection, the malware creates new instances of [[explorer.exe]] and [[svchost.exe]] to communicate with its servers. When encrypting files, the malware also deletes volume shadow copies, and installs spyware that steals passwords and [[Bitcoin wallet]]s.<ref name=tm-cw3>{{cite web|title=CryptoWall 3.0 Ransomware Partners With FAREIT Spyware|url=http://blog.trendmicro.com/trendlabs-security-intelligence/cryptowall-3-0-ransomware-partners-with-fareit-spyware/|publisher=Trend Micro|accessdate=25 June 2015}}</ref>

The FBI reported in June 2015 that nearly 1,000 victims had contacted the bureau's [[Internet Crime Complaint Center]] to report CryptoWall infections, and estimated losses of at least $18 million.<ref name=ars-fbicryptowall>{{cite web|title=FBI says crypto ransomware has raked in >$18 million for cybercriminals|url=http://arstechnica.com/security/2015/06/fbi-says-crypto-ransomware-has-raked-in-18-million-for-cybercriminals/|website=Ars Technica|accessdate=25 June 2015}}</ref>

The most recent version, CryptoWall 4.0, enhanced its code to avoid antivirus detection, and encrypts not only the data in files but also the file names.<ref name=heimdal>{{cite web |date=5 November 2015 |author=Andra Zaharia |title=Security Alert: CryptoWall 4.0 – new, enhanced and more difficult to detect |url=https://heimdalsecurity.com/blog/security-alert-cryptowall-4-0-new-enhanced-and-more-difficult-to-detect/ |website=HEIMDAL |accessdate=5 January 2016}}</ref>

=== Fusob ===
Fusob is one of the major mobile ransomware families. Between April 2015 and March 2016, about 56 percent of accounted mobile ransomwares was Fusob.<ref>{{cite web|title=Ransomware on mobile devices: knock-knock-block|url=https://blog.kaspersky.com/mobile-ransomware-2016/12491/|website=Kaspersky Lab |accessdate=4 Dec 2016}}</ref>

Like a typical mobile ransomware, it employs scare tactics to extort people to pay a ransom.<ref>{{cite web|title=The evolution of mobile ransomware
|url=https://blog.avast.com/the-evolution-of-mobile-ransomware|website=Avast|accessdate=4 Dec 2016}}</ref> The program pretends to be an accusatory authority, demanding the victim to pay a fine from $100 to $200 [[United States Dollar|USD]] or otherwise face a fictitious charge. Rather surprisingly, Fusob suggests using iTunes gift cards for payment. Also, a timer clicking down on the screen adds to the users’ anxiety as well.

In order to infect devices, Fusob [[Trojan (computing)|masquerades]] as a pornographic video player. Thus, victims, thinking it is harmless, unwittingly download Fusob.<ref>{{cite web|title=Mobile ransomware use jumps, blocking access to phones
|url=http://www.pcworld.com/article/3090049/security/mobile-ransomware-use-jumps-blocking-access-to-phones.html|website=PCWorld|publisher=IDG Consumer & SMB |accessdate=4 Dec 2016}}</ref>

When Fusob is installed, it first checks the language used in the device. If it uses Russian or certain Eastern European languages, Fusob does nothing. Otherwise, it proceeds on to lock the device and demand ransom. Among victims, about 40% of them are in Germany with the United Kingdom and the United States following with 14.5% and 11.4% respectively.

Fusob has lots in common with Small, which is another major family of mobile ransomware. They represented over 93% of mobile ransomwares between 2015 and 2016.

=== WannaCry ===
{{main|WannaCry ransomware attack}}
In May 2017, the [[WannaCry ransomware attack]] spread through the Internet, using an exploit vector that Microsoft had issued a "Critical" patch for ([https://technet.microsoft.com/en-us/library/security/ms17-010.aspx MS17-010]) two months before on March 14, 2017. The ransomware attack infected over 75,000 users in over 99 countries, using 20 different languages to demand money from users using [[Bitcoin]] cryptocurrency. The attack affected [[Telefónica]] and several other large companies in Spain, as well as parts of the British [[National Health Service]] (NHS), where at least 16 hospitals had to turn away patients or cancel scheduled operations,<ref>{{cite web|url=https://www.theguardian.com/society/2017/may/12/global-cyber-attack-nhs-trusts-malware|title=The NHS trusts hit by malware – full list|first=Sarah|last=Marsh|date=12 May 2017|publisher=|accessdate=12 May 2017|via=The Guardian}}</ref> [[FedEx]], [[Deutsche Bahn]], as well as the [[Ministry of Internal Affairs (Russia)|Russian Interior Ministry]] and Russian telecom [[MegaFon]].<ref name=":2">{{Cite news|url=https://www.rt.com/news/388153-thousands-ransomeware-attacks-worldwide/|title=Ransomware virus plagues 75k computers across 99 countries|work=RT International|access-date=2017-05-12|language=en-US}}</ref>

== Mitigation ==
As with other forms of malware, security software might not detect a ransomware payload, or, especially in the case of encrypting payloads, only after encryption is under way or complete, particularly if a [[Zero-day exploit|new version unknown to the protective software]] is distributed.<ref name=yumasun-cryptolocker>{{cite news|title=Yuma Sun weathers malware attack|url=http://www.yumasun.com/news/local/article_f38f14e8-4f50-11e3-8165-0019bb30f31a.html|accessdate=18 August 2014|work=[[Yuma Sun]]}}</ref> If an attack is suspected or detected in its early stages, it takes some time for encryption to take place; immediate removal of the malware (a relatively simple process) before it has completed would stop further damage to data, without salvaging any already lost.<ref name=malwarebytes>{{cite web|last=Cannell|first=Joshua|title=Cryptolocker Ransomware: What You Need To Know, last updated 06/02/2014|url=http://blog.malwarebytes.org/intelligence/2013/10/CryptoLocker-ransomware-what-you-need-to-know/|work=Malwarebytes Unpacked|accessdate=19 October 2013}}</ref><ref name=register>{{cite web|last=Leyden|first=Josh|title=Fiendish CryptoLocker ransomware: Whatever you do, don't PAY|url=http://www.theregister.co.uk/2013/10/18/cryptolocker_ransmware|work=The Register|accessdate=18 October 2013}}</ref>

Alternately, new categories of security software, specifically [[deception technology]], can detect ransomware without using a signature-based approach. Deception technology utilizes fake SMB shares which surround real IT assets. These fake SMB data shares deceive ransomware, tie the ransomware up encrypting these false SMB data shares, alert and notify cyber security teams which can then shut down the attack and return the organization to normal operations. There are multiple vendors<ref>{{Cite web|url=http://www.itwire.com/security/73914-deception-%E2%80%93-the-best-offense-against-cyber-attack.html|title=The Best Defense Against Cyber Attack|last=Shaw|first=Ray|date=July 20, 2016|website=IT Wire|publisher=itwire.com|access-date=December 10, 2016}}</ref> that support this capability with multiple announcements in 2016.<ref>{{Cite web|url=http://www.information-management.com/news/security/tool-turns-tables-on-ransomware-10029614-1.html|title=Tool Turns Tables on Ransomware|last=Goedert|first=Joseph|date=August 26, 2016|website=information-management.com|publisher=Information Management|access-date=December 10, 2016}}</ref>

Security experts have suggested precautionary measures for dealing with ransomware. Using software or other security policies to block known payloads from launching will help to prevent infection, but will not protect against all attacks. Keeping "offline" backups of data stored in locations inaccessible to the infected computer, such as external storage drives, prevents them from being accessed by the ransomware, thus accelerating data restoration.<ref name="ars-cryptolocker" /><ref name="securityweek131119">{{cite web 
| url = http://www.securityweek.com/cryptolocker-infections-rise-us-cert-issues-warning
| title = Cryptolocker Infections on the Rise; US-CERT Issues Warning
| date = 19 November 2013
| work = SecurityWeek
| accessdate = 18 January 2014
}}</ref>

There are a number of tools intended specifically to decrypt files locked by ransomware, although successful recovery may not be possible.<ref name=schofield>{{cite web |url=https://www.theguardian.com/technology/askjack/2016/jul/28/how-can-i-remove-ransomware-infection |title=How can I remove a ransomware infection? |newspaper=The Guardian |date=28 July 2016  |author=Jack Schofield|accessdate= 28 July 2016}}</ref><ref>{{cite web |url=http://www.thewindowsclub.com/list-ransomware-decryptor-tools |title=List of free Ransomware Decryptor Tools to unlock files |website=Thewindowsclub.com |date=  |author= |accessdate= 28 July 2016}}</ref> If the same encryption key is used for all files, decryption tools use files for which there are both uncorrupted backups and encrypted copies (a [[known-plaintext attack]] in the jargon of [[cryptanalysis]]); recovery of the key, if it is possible, may take several days.<ref>{{cite web |url=http://www.thewindowsclub.com/emsisoft-decrypter-hydracrypt-umbrecrypt-ransomware |title=Emsisoft Decrypter for HydraCrypt and UmbreCrypt Ransomware |website=Thewindowsclub.com |date=  |author= |accessdate= 28 July 2016}}</ref>

== See also ==
{{portal|Computer security}}
* [[Phishing]]

== References ==
{{reflist|30em}}

== Further reading ==
* {{cite book|author=A. Young, [[Moti Yung|M. Yung]]|title=Malicious Cryptography: Exposing Cryptovirology|publisher=Wiley|year=2004|isbn=0-7645-4975-8}}
* {{cite web | last = [[Mark Russinovich|Russinovich]] | first = Mark | title = Hunting Down and Killing Ransomware (Scareware) | publisher = ''Microsoft TechNet blog'' | date = 7 January 2013 | url = http://blogs.technet.com/b/markrussinovich/archive/2013/01/07/3543763.aspx}}
* {{cite web | last =  Simonite  | first = Tom | title = Holding Data Hostage: The Perfect Internet Crime? Ransomware (Scareware) | publisher = ''[[MIT Technology Review]]''  | date = 4 February 2015 | url = http://www.technologyreview.com/news/534516/holding-data-hostage-the-perfect-internet-crime/}}
* {{cite web | last = Brad | first = Duncan | title = Exploit Kits and CryptoWall 3.0 | publisher = The Rackspace Blog! & NewsRoom | date = 2 March 2015 | url = http://www.rackspace.com/blog/exploit-kits-and-cryptowall-3-0/}}
*{{cite web
 | publisher = The Federal Bureau of Investigation JANUARY 2015| url=https://www.fbi.gov/news/stories/2015/january/ransomware-on-the-rise
 | title= Ransomware on the Rise
}}
*{{cite web
 | author=Yang, T.| author2=Yang, Y.| author3=Qian, K.| author4=Lo, D.C.T.| author5=Qian, L.| author6=Tao, L.| last-author-amp=yes
 | url=http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=7336353&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D7336353
 | title= Automated Detection and Analysis for Android Ransomware
 | publisher=IEEE Internet of Things Journal, CONFERENCE, AUGUST 2015
}}
*{{cite web
 | author=Richet, Jean-Loup| last-author-amp=yes
 | url=https://blogs.harvard.edu/jeanlouprichet/files/2015/07/Extortion_on_the_Internet_Rise_of_Crypto_Ransomware.pdf
 | title= Extortion on the Internet: the Rise of Crypto-Ransomware
 | publisher=Harvard
}}

==External links==
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*[http://www.cryptovirology.com Cryptovirology Labs website]
*[https://www.fbi.gov/news/stories/2015/january/ransomware-on-the-rise Incidents of Ransomware on the Rise] – [[Federal Bureau of Investigation]]
*[http://frontrowcrew.com/geeknights/20160418/ransomware/ Geeknights 20160418: Ransomware]
{{Software distribution}}
{{Malware}}

Gsn{{good article}}

[[Category:Ransomware| ]]
[[Category:Types of malware]]