A computer virus is a piece of malicious computer software (malware) which attempts to copy itself into existing executable files on a computer. By doing this, the virus hijacks the file's execution. Computer viruses generally attempt to destroy software and operating systems, but usually not before spreading themselves to other devices.
Methods of transmission
- Automatic replication: When an infected program is run, the virus also runs, searching the host computer for other programs to infect.
- By email: viruses (and other kinds of malware) are often transmitted as email attachments. In some cases, scripts within a message can also be used to infect a device, if the E-mail client program is not configured to ignore scripts.
- Misleading software: A "Trojan Horse" is a program which seems useful, but contains a virus or other malware. The main program may or may not perform as advertised, but the distributor knows it is infected. A Trojan Horse carried virus typically does not replicate itself but is spread when the user copies the program. In some cases, legitimate software may also be infected after release. Even though the software by itself is legitimate and safe, infected copies can be distributed to attack unsuspecting users.
- Instant messaging: A direct computer-to-computer link required for instant messaging can be misused to deliver a virus.
Configuring email software so that it never runs attached programs or embedded scripts is an easy way to stop email-transmitted viruses. This should be the default setting, especially for corporate systems.
Computer users should also be aware that free games and other such scripts available on the Internet can be risky to use. Reputable software companies go to great lengths to ensure virus-free software, so it is wise to stick with these whenever possible. Using a designated computer (or virtual system) is a safer way to experiment with such higher-risk internet services.
A virus is technically a type of software which acts very much like a biological virus; the term refers to a specific kind of malware which infects preexisting files. However, since virus attacks became well known before most other types malware attacks, many people use the term "virus" for any kind of malicious software. Although this is technically incorrect, it is common for someone to call anything unwanted, such as adware, a virus.