Viruses are malicious computer programs used to gather information and destroy other computers. Viruses spread over the Internet and removable media, etc.
Viruses are a type of software known as malware, which is software intended to act against the user or use their system for malicious purposes. A computer running malware, including viruses, is said to be infected. Viruses will typically hijack infected machines to produce more copies of themselves and spread to other computers using a variety of transmission methods.
The term "virus" is often incorrectly used to refer to malware in general. In addition, viruses can be further differentiated into different types:
- Trojan horse: What appears to be a legitimate program, but hides a malicious payload that is unleashed when the user runs it.
- Rogue antivirus: A recent type of Trojan horse which purports to be a genuine antivirus program. They typically trick users by "scanning" their system and showing a list of false positives or other viruses they planted there, and ask the user to install them and pay the creators money for a bogus antivirus subscription.
- Worm: A virus that is able to spread itself across a network by utilizing security holes in unpatched systems. A worm differs from an ordinary virus in that the latter may require additional action on the user's part to spread, while a worm does not.
Other types of malware that may not be considered viruses include rootkits, adware, and spyware.
Many older viruses proudly announced their presence on affected systems by displaying strange messages or causing odd errors and data loss, having been produced by immature programmers looking for a way to show off their skills or prank people. However, most modern viruses are stealthier and far more sinister, having been developed by professional criminals with some sort of serious goal in mind, such as creating a botnet.
Malware authors typically write their software to target security vulnerabilities and systems with a large market share, so they can infect as many computers as possible. This explains why the most commonly affected systems run Windows or Android, although there has been a recent rise in Mac viruses as well. Linux systems such as Ubuntu typically don't face a threat from viruses due to the relatively rapid rate at which security vulnerabilities get patched and low market share among desktop users, although Linux viruses do exist.
The best ways any user can protect themselves from malware is to:
- Apply system updates as they are released, especially security fixes.
- Run a legitimate antivirus product and keep its signatures up-to-date.
- Avoid running suspicious software.
See http://en.wikipedia.org/wiki/Computer_virus for more information.
