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.
Allegations of aggressive advertising (distribution via drive-by downloads) and false positives to goad purchase. Third parties document relationships with other "rogue" applications: #1 Spyware Killer, Max Privacy Protector, SpyDoctor, SpyFirewall, Spyinator, SpyKiller 2005, SpyLax, SpywareThis, & Spyware Protection Pro.
Site Advisor Advisory: "Feedback from credible users indicates this site engaged in one or more negative or undesired activities."
For additional information consult these references: