An uninstaller is a PC application that is designed to completely remove all the parts of a specific application. It is the reverse of an installer. A third-party uninstaller, such as Perfect Uninstaller, is an example of an application that uninstalls other programs.

Most commercial software vendors ship an uninstall program with their software, but these program removers commonly lack completeness. The quandary with the application specific uninstall feature is that this feature is usually built at the end of the program development phase when the developers are in a sprint to complete their debug and testing to get the product finished. Also, as programs get more complex and often integrate third-party components, many of these components are forgotten about by the programmers and without time to complete their testing the uninstaller function they leave remnants behind when the software is deleted. Application development companies do not care about the quality of the uninstaller’s capability as they make their money on the program install and use. The uninstall capability is typically an after thought.

With Internet access generally accessible, many computer users download free applications. Users should be cautious only to download applications from known and trusted sources, as many at no cost programs might be spyware programs disguised as useful utilities. Additionally, many freeware programs can come bundled with all types of add ons that are purposefully left behind on the users PC after the main application is removed. These scraps continue to clutter the PC hard drive and, in many cases, are still running in the background and slow down the PC's operation.

The components of an uninstaller typically include the following:

• Uninstaller: a program remover reverses the modifications that the program made during installation. The uninstaller feature is the capability of the application and uses information collected through the logger and analyzer to find out what files and registry entries to remove. Since the vital functions of the uninstaller program are well understood within the software industry, the algorithms and monitor / detection components that are used by uninstalling software is currently what makes the distinction commercial uninstallers from each other.

• Logger: The logger monitors which files and registry entries were added and changed when an application is installed (i.e., it logs what happens during installation). This log information can be used later when the computer user decides to delete the application and revert the PC to state before the installation.

• Analyzer: The analyzer capability is where most freeware applications come up short. When an application was installed earlier than the third-party uninstaller was purchased, the uninstall software relies on the analyzer function to read through the system files and registry to find out where the programs components are found and are their additional applications that use those components. If other programs are not using these files then they will be removed. If other programs need the same system file then it is better to leave the file behind.

• Miscellaneous functions: With the competition in the standalone uninstaller software business, many applications have started to differentiate themselves with complementary add on tools like junk file cleaner, browser history cleaner, browser cache cleaner, etc. These functions are not directly required by the core uninstaller utility, but are added to improve the end users experience by adding hard drive cleaning functions.

Perfect Uninstaller, a well known uninstall application, includes the uninstaller, logger, and analyzer capabilities as well as many additional add-on cleaner utilities.