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.
Claims to be an adware remover.
It drive-by installs, phones home after install, gives itself the right (in the EULA) to download and install software from its servers, and you have to *pay them* for a "subscription" with a credit card to have it removed, then opt out of having the "subscription" automatically renewed.
Because you must pay to have to removed, some have dubbed this "extortion ware".
Can sometimes be removed by using Add/Remove programs from the control panel.