Parasiteware refers to any software or program that infects a computer in order to perform various malicious activities, which often entails displaying aggressive and unsolicited advertisements. Parasiteware maliciously advertises or promotes a product on the host computer desktop and/or within its Internet browsing.
Techopedia explains Parasiteware
Parasiteware is often a type of adware software that has been infected or illegally modified by a cracker. Parasiteware is typically installed as a bundled application with freeware applications. Although parasiteware is known to exhibit different behaviors, its primary objective is to alter the affiliate IDs in adware to point to different affiliate IDs. In addition, parasiteware might also display advertisements on the user's desktop, alter the browser tool bars and continuously send advertisement-based pop-up messages.