Examine individual changes

'{{refimprove|date=December 2008}} {{Expand|date=November 2009}} [[Image:Registry Editor Vista.png|right|thumb|The ''Registry Editor'' in [[Windows Vista]]]] A '''registry cleaner''' is a type of software utility designed for the [[Microsoft Windows]] [[operating system]] whose purpose is to remove redundant or unwanted items from the [[Windows registry]]. However the necessity and usefulness of registry cleaners is a controversial topic, with experts not agreeing on their benefit. The problem is further clouded by the fact that [[malware]] and [[scareware]] is often associated with utilities of this type. ==Purpose== Registry Cleaners are software utilities that attempt to remove configuration data from the Windows Registry that is no longer in use or that is unwanted on the system. Such data may include information left by software that has not been uninstalled completely from the computer, information that is no longer of use, or settings required for the operation of [[malware]]. A registry cleaner scans the registry, and attempts to pick out the unnecessary values in order to delete or repair them. ==Advantages== Registry cleaners, or registry cleanup software, may improve the performance of computers by ridding the registry of redundant information.{{Citation needed|date=December 2008}} Due to the sheer size and complexity of the registry database, manually cleaning up debris and invalid entries would be impractical, so registry cleaners are essentially tools that automate the process of looking for invalid entries, missing file references or broken links within the registry and resolving them. The correction of an invalid registry key can provide some benefits.{{Citation needed|date=December 2008}} For example, on older versions of Windows, a registry entry indicating a program should be run at startup from a network path that no longer exists can delay startup by as long as the network protocol takes to timeout. Noted Windows architecture expert [[Mark Russinovich]] has concluded that registry cleaners will continue to have a role until most applications have moved to the [[.NET Framework]] platform that does not rely on the registry for application settings.<ref>{{cite web|url=http://blogs.technet.com/markrussinovich/archive/2005/10/02/registry-junk-a-windows-fact-of-life.aspx|title=Registry Junk: A Windows Fact of Life|accessdate=2008-06-21|publisher=[http://blogs.technet.com Mark Russinovich]}}</ref> Some registry cleaners offer backup and restore functions that allow the user to revert changes made by the registry cleaner in case they are undesired. A registry cleaner may be useful for someone that adds or removes programs from their computer very often; however, a [[virtual machine]] is a faster and more reliable means of reverting an operating system to a previous good known state in a testing scenario. ==Disadvantages== Some registry cleaners make no distinction as to the severity of the errors, and many that do may erroneously categorize errors as "critical" with little basis to support it—a modern form of [[snake oil]].{{Citation needed|date=May 2009}} ===Registry damage=== Most notably, critics say there is no reliable way for a [[Third-party developer|third party]] program to know whether any particular key is invalid, redundant or neither. Poorly designed registry cleaners may not know for sure whether a key is still being used by Windows or what detrimental effects removing it may have. This has led to examples of registry cleaners causing loss of functionality and/or system instability,<ref>{{cite web|url=http://service1.symantec.com/SUPPORT/sunset-c2002kb.nsf/pfdocs/2001142275577966?OpenDocument&Src=bar_sch_nam&docid=2001142275577966|title=Error: "Internet Explorer Script Error..." when scanning after running a registry cleanup utility|publisher=[[Symantec]]|accessdate=2008-05-19|date=October 2, 2002}}</ref><ref>{{cite web|url=http://support.microsoft.com/kb/951950|title=The .NET Framework 2.0 SP1 installation fails on a computer that has the .NET Framework 2.0 installed and that is running Windows XP, Windows Server 2003, or Windows 2000|date=April 24, 2008|accessdate=2008-05-19|publisher=[[Microsoft]]}}</ref><ref>{{cite web|url=http://support.microsoft.com/kb/247678|title=OL2000: Error Message: "Outlook Caused an Invalid Page Fault in Module Msvcrt.dll" When Creating an Appointment|date=November 5, 2003|accessdate=2008-05-19|publisher=[[Microsoft]]}}</ref> as well as [[shim (computing)|application compatibility updates]] from Microsoft to block problematic Registry cleaners.<ref>{{cite web|url=http://support.microsoft.com/KB/972036|title=August 2009 Windows Vista and Windows Server 2008 Application Compatibility Update|date=2009-09-01|accessdate=2009-09-25|publisher=[[Microsoft]]}}</ref> ===Malware payloads=== The benefits of Registry cleaners have been used by a number of [[Trojan horse (computing)|trojan]] applications to install [[malware]], typically through "social engineering" attacks that use website [[pop-up ad|popups]]. Rogue registry cleaner "[[WinFixer]]" has been ranked as one of the most prevalent pieces of malware currently in circulation.<ref>{{cite web|url=http://www.stopbadware.org/reports/reportdisplay?reportname=winfixer|publisher=StopBadware.Org|accessdate=2008-06-21|title=WinFixer}}</ref> ===Scareware=== Rogue registry cleaners are often marketed with alarmist advertisements that falsely claim to have pre-analyzed your PC, displaying bogus warnings to take "corrective" action, hence the reason that they are sometimes called "[[scareware]]". In October 2008, [[Microsoft]] and the [[Washington]] [[attorney general]] filed a lawsuit against two Texas firms, Branch Software and Alpha Red, producers of the "Registry Cleaner XP" scareware.<ref>{{cite news|url=http://news.bbc.co.uk/2/hi/technology/7645420.stm|title=Fighting the scourge of scareware|date=2008-10-01|accessdate=2008-10-02|publisher=[[BBC News]]}}</ref> The lawsuit alleges that the company sent incessant pop-ups resembling system warnings to consumers' personal computers stating "CRITICAL ERROR MESSAGE! - REGISTRY DAMAGED AND CORRUPTED", before instructing users to visit a web site to download Registry Cleaner XP at a cost of $39.95. ===Marginal performance benefit=== On [[Windows 9x]] computers, it is possible that a very large registry could slow down the computer's startup time. However this is far less of an issue with [[Windows NT|NT]]-based operating systems (including Windows XP and Vista) due to a different on-disk structure of the registry, improved memory management and [[index (database)|indexing]].<ref>{{cite web | url = http://msdn.microsoft.com/msdnmag/issues/1100/Registry/ | title = Windows 2000 Registry: Latest Features and APIs Provide the Power to Customize and Extend Your Apps | accessdate = 2007-07-19}}</ref> Slowdown due to registry bloat is thus far less of an issue in modern versions of Windows. More importantly, however, the difference in speed due to the use of a registry cleaner is negligible: rarely do they remove more than a few kilobytes from the total size of the registry. In fact, technology journalist Ed Bott has claimed that no one has ever successfully managed to measure any significant performance increase from the use of a registry cleaner.<ref>[http://www.edbott.com/weblog/archives/000643.html ''Why I don’t use registry cleaners'', Ed Bott]</ref> Even so, there are reviews showing different performance benefits for various registry cleaner products.<ref>[http://www.registrycleanergeeks.com/]</ref> Any potential user of a registry cleaner must thus balance a probably negligible performance increase against the possibility of system instability. A safer and more measurable approach to registry performance is to defragment the registry files using a Microsoft-supported tool such as [[PageDefrag]].<ref>{{cite web|url=http://technet.microsoft.com/en-us/magazine/cc137806.aspx|title=Utility Spotlight PageDefrag|author=Lance Whitney|publisher=[[Microsoft]]|date=September 2007|accessdate=2008-08-29}}</ref> ===Malware removal=== Registry cleaners are not specialized malware removal utilities, and therefore are not equipped to deal with complex scenarios where malware such as [[spyware]], [[adware]] and [[computer virus|viruses]] can re-infect a computer through multiple infection vectors, where removal results in system instability or infection of the tool itself. A registry cleaner cannot detect or remove registry entries associated with a [[rootkit]], which will hide this information from other processes. A specialized tool such as RootkitRevealer is required to compare the results returned by Registry API's against the raw underlying registry storage.<ref>{{cite web|url=http://technet.microsoft.com/en-us/sysinternals/bb897445.aspx|title=RootkitRevealer v1.71|author=Bryce Cogswell and Mark Russinovich|date=2006-11-01|accessdate=2008-12-08|publisher=[[Microsoft]]}}</ref> ===Application virtualization=== A registry cleaner is of no use for cleaning registry entries associated with a [[application virtualization|virtualised application]] since all registry entries in this scenario are written to an application-specific virtual Registry instead of the real one.<ref>{{cite web|url=http://technet.microsoft.com/en-us/magazine/2008.10.appv.aspx|title=Getting Started with Microsoft Application Virtualization|publisher=[[Microsoft]]|author=Anthony Kinney|accessdate=2009-01-06}}</ref> ==References== {{reflist}} == External links == <!--===========================({{NoMoreLinks}})===============================--> <!--| DO NOT ADD MORE LINKS TO THIS ARTICLE. WIKIPEDIA IS NOT A COLLECTION OF |--> <!--| LINKS. If you think that your link might be useful, do not add it here, |--> <!--| but put it on this article's discussion page first or submit your link |--> <!--| to the appropriate category at the Open Directory Project (www.dmoz.org)|--> <!--| and link back to that category using the {{dmoz}} template. |--> <!--| |--> <!--| Links that have not been verified WILL BE DELETED. |--> <!--| See [[Wikipedia:External links]] and [[Wikipedia:Spam]] for details |--> <!--===========================({{NoMoreLinks}})===============================--> [[Category:Windows-only software]]'