Computer virus

A computer virus^[1] is a type of malware that, when executed, replicates itself by modifying other computer programs and inserting its own code into those programs.^[2][3] If this replication succeeds, the affected areas are then said to be "infected" with a computer virus, a metaphor derived from biological viruses.^[4]

Computer viruses generally require a host program.^[5] The virus writes its own code into the host program. When the program runs, the written virus program is executed first, causing infection and damage. By contrast, a computer worm does not need a host program, as it is an independent program or code chunk. Therefore, it is not restricted by the host program, but can run independently and actively carry out attacks.^[6][7]

Virus writers use social engineering deceptions and exploit detailed knowledge of security vulnerabilities to initially infect systems and to spread the virus. Viruses use complex anti-detection/stealth strategies to evade antivirus software.^[8] Motives for creating viruses can include seeking profit (e.g., with ransomware), desire to send a political message, personal amusement, to demonstrate that a vulnerability exists in software, for sabotage and denial of service, or simply because they wish to explore cybersecurity issues, artificial life and evolutionary algorithms.^[9]

As of 2013, computer viruses caused billions of dollars' worth of economic damage each year.^[10] In response, an industry of antivirus software has cropped up, selling or freely distributing virus protection to users of various operating systems.^[11]