These are usually anti-spyware or security software applications that use various forms of deception and/or unethical means or show a history of negligent false positives to goad the end user to make a purchase.
In some cases these applications maybe downloaded with some form of unwanted software at which point the rogue application is offered to the customer as a way to remove the unwanted software.
SpyOnThis affiliate claims "...SpyOnThis is a powerful alternative to HijackThis for anyone facing problems with Spyware, Adware, and Hijackers on their PC...".
Once installed it will provide many erroneous results in a clean Windows Operating System. Will not let you remove the program unless you purchase the full version. No valid uninstaller found in Windows Add and Remove programs. Uninstaller found in SpyOnThis program directory, but does not perform a complete uninstall.
Also listed at: http://www.spywarewarrior.com/rogue_anti-spyware.htm