Coined as a term in September 2004, grayware (or greyware) refers to an unwanted software program (small or large) that can cause damage to a computer system. Most adware, malware, and spyware programs can be classified as grayware. In general, grayware is not as destructive as a virus, but rather are more of a nuisance or annoyance.
Grayware can generate pop-up ads, cause security vulnerabilities on a computer or network, and can potentially prohibit users from performing certain actions. Anti-spyware and anti-malware programs can be used to remove grayware and help prevent future grayware from infecting a computer.