The worst of the breed are products that advertise and encourage a 'free' Registry scan however, the user typically finds the product has to be purchased for a substantial sum, before it will effect any of the anticipated 'repairs'. Registry cleaners have been used as a vehicle by a number of trojan applications to install malware, typically through social engineering attacks that use website pop-up ads or free downloads that falsely report problems that can be 'rectified' by purchasing or downloading a Registry cleaner. The Windows Installer CleanUp Utility was a Microsoft-supported utility for addressing Windows Installer related issues. This may lead to loss of functionality and/or system instability, as well as application compatibility updates from Microsoft to block problematic Registry cleaners. A poorly designed Registry cleaner may not be equipped to know for sure whether a key is still being used by Windows or what detrimental effects removing it may have. It is not always possible for a third-party program to know whether any particular key is invalid or redundant. Removing or changing certain Registry data can prevent the system from starting, or cause application errors and crashes.

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.

The correction of an invalid Registry key can provide some benefits but the most voluminous will usually be quite harmless, obsolete records linked with COM-based applications whose associated files are no longer present. ( December 2014) ( Learn how and when to remove this template message)ĭue to the sheer size and complexity of the Registry database, manually cleaning up redundant and invalid entries may be impractical, so Registry cleaners try to automate the process of looking for invalid entries, missing file references or broken links within the Registry and resolving or removing them. Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This section needs additional citations for verification.

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