Advantages and Disadvantages of Registry Cleaners

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.

Over time, the Windows Registry can begin to contain information that's no longer valid. Maybe you uninstalled an application without using the Add or Remove Programs function in the Control Panel, or perhaps an object or file in the registry got moved. Eventually this orphaned or misplaced information accumulates and begins to clog your registry, potentially slowing down your PC and causing error messages and system crashes. You might also notice that your PC's startup process is slower than it used to be. A registry cleaner is the easiest way to help avoid these common problems.

However, the necessity and usefulness of registry cleaners is a controversial topic, with experts in disagreement over their benefit. The problem is further clouded by the fact that malware and scareware are often associated with utilities of this type.

Advantages
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. 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.

Some registry cleaners offer backup and restore functions that allow the user to revert changes made by the registry cleaner in the event that it breaks functionality. A registry cleaner may be useful for someone that adds or removes programs from their computer very often; however, a virtual machine or virtual application 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.

Removing certain registry data can prevent the system from starting, or cause errors and crashes.
Registry damage

Most notably, critics say there is no reliable way for a third party program to know whether any particular key is invalid or redundant. 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, as well as application compatibility updates from Microsoft to block problematic registry cleaners. The Windows Installer Clean Up Utility is a Microsoft-supported utility for addressing Windows Installer related issues.

Malware payloads

Message from WinFixer attempting to dupe a user into buying the scareware product
The benefits of Registry cleaners have been used by a number of trojan applications to install malware, typically through social engineering attacks that use website popups or free downloads that falsely report problems that can be rectified by purchasing a registry cleaner. Rogue registry cleaner "WinFixer" has been ranked as one of the most prevalent pieces of malware currently in circulation.

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 NT-based operating systems (including Windows XP and Vista) due to a different on-disk structure of the registry, improved memory management and indexing. 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. 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, or to use the Windows Performance Tools, which are specifically designed to troubleshoot performance-related issues under Windows.

Undeletable registry keys

Registry cleaners cannot repair scenarios such as undeletable registry keys caused by embedded null characters in their names; only specialized tools such as the RegDelNull utility (part of the Sysinternals software) are able to do this.

Recovery capability

A Registry cleaner cannot repair a Registry hive that can't be mounted by the system. However a corrupt registry can be recovered in a number of ways that are supported by Microsoft.

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 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 Rootkit Revealer is required to compare the results returned by Registry API's against the raw underlying registry storage.

Application virtualization

A registry cleaner is of no use for cleaning registry entries associated with a virtualised application since all registry entries in this scenario are written to an application-specific virtual Registry instead of the real one.

Though registry cleaners’ disadvantages seem overweight the advantages, there are huge market for their use as long as the computers perform slow or corrupt often.