Malware

Malware (a portmanteau of "malicious software") is any software developed for the purpose of doing harm to a computer system.

Malware can be classified based on how it is executed, how it spreads, and/or what it does. The classification is not perfect, however, in the sense that the groups often overlap and the difference is not always obvious, giving rise to frequent flame wars.

A number of spyware remover applications are available to help computer users search for and remove Malware software.

Additional Definitions:

Adware
Browser Hijacker
Dialer
Malware
Scumware
Spyware
Trojan Horse
Virus
Worm