A computer virus is a computer program that can copy itself and infect acomputer. 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 the reproductive ability. A true virus can spread from one computer to another (in
some form of executable code) when its host is taken to the target computer; for instance
because a user sent it over a network or the Internet, or carried it on a removable medium
such as a floppy disk, CD, DVD, or USB drive.
Viruses can increase their chances of spreading to other computers by infecting
files on a network file system or a file system that is accessed by another computer.
As stated above, the term “computer virus” is sometimes used as a catch-all
phrase to include all types of malware, even those that do not have the reproductive
ability. Malware includes computer viruses, computer worms, Trojan horses, most
rootkits, spyware, dishonest adware and other malicious and unwanted software,
including true viruses. Viruses are sometimes confused with worms and Trojan horses,
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,