Malware, short for malicious software, is software used or created by hackers to disrupt computer operation, gather sensitive information, or gain access to private computer systems. While it is often software, it can also appear in the form of scripts or code. 'Malware' is a general term used to refer to a variety of forms of hostile, intrusive, or annoying software.
Malware includes computer viruses, worms, trojan horses, spyware, adware, most rootkits, and other malicious programs. In law, malware is sometimes known as a computer contaminant, as in the legal codes of several U.S. states. Malware is not the same as defective software, which is software that has a legitimate purpose but contains harmful bugs that were not noticed before release. However, some malware is disguised as genuine software, and may come from an official company website. An example would be software used for harmless purposes that also includes tracking software to gather marketing statistics for advertising by the software producer. Therefore, some security programs may find "potentially unwanted programs" when scanning for malware. While a computer virus is malware that can reproduce itself, the term is sometimes used incorrectly to refer to the entire category. An example of a computer virus which is not a malware, but is benevolent is Fred Cohen's compression virus.