A computer virus is a computer program that can replicate
itself and spread from one computer to another. The term "virus" is
also commonly, but erroneously, used to refer to other types of malware,
including but not limited to adware and spyware programs that do not have a
reproductive ability.
Malware includes computer viruses, computer worms,
ransomware, trojan horses, keyloggers, most rootkits, spyware, dishonest
adware, malicious BHOs and other malicious software. The majority of active
malware threats are usually trojans or worms rather than viruses. Malware such
as trojan horses and worms is sometimes confused with viruses, which are
technically different: a worm can exploit security vulnerabilities to spread
itself automatically to other computers through networks, while a trojan horse
is a program that appears harmless but hides malicious functions. Worms and
trojan horses, like viruses, may harm a computer system's data or performance.
Some viruses and other malware have symptoms noticeable to the computer user,
but many are surreptitious or simply do nothing to call attention to
themselves. Some viruses do nothing beyond reproducing themselves.
