Computer program that modifies other programs to replicate itself and spread
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]
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]
Ludwig, Mark A. (1996). The Little Black Book of Computer Viruses: Volume 1, The Basic Technologies. American Eagle Publications. pp. 16–17. ISBN0-929408-02-0.