Foistware is software that is installed without permission, and so is foisted upon unsuspecting users. It typically is spyware or adware, and is often hard to uninstall. Examples of this are Gator and These are not viruses or trojans, and usually have no intentional malicious effects. Some foistware allows other foistware to be installed. There are programs to remove it, but these are not entirely effective, and they are far from ubiquitous.