| A computer virus is a self-replicating computer | | | | popularly traded software. Shareware and bootleg |
| program written to alter the way a computer | | | | software were equally common vectors for viruses |
| operates, without the permission or knowledge of the | | | | on BBS's. |
| user. | | | | Since the mid-1990s, macro viruses have become |
| Elk Cloner is credited with being the first computer | | | | common. Most of these viruses are written in the |
| virus to appear "in the wild" -- outside the single | | | | scripting languages for Microsoft programs such as |
| computer or lab where it was created. Written in 1982 | | | | Word and Excel. These viruses spread in Microsoft |
| by Rich Skrenta, it attached itself to the Apple DOS | | | | Office by infecting documents and spreadsheets. |
| 3.3 operating system and spread by floppy disk. The | | | | Since Word and Excel were also available for Mac |
| first PC virus was a boot sector virus called (c)Brain, | | | | OS, most of these viruses were able to spread on |
| created in 1986 by two brothers, Basit and Amjad | | | | Macintosh computers as well. |
| Farooq Alvi, Pakistan. The brothers reportedly created | | | | A computer virus may also be transmitted through |
| the virus to deter pirated copies of software they had | | | | instant messaging. A virus may send a web address |
| written. | | | | link as an instant message to all the contacts on an |
| Before computer networks became widespread, most | | | | infected machine. If the recipient, thinking the link is from |
| viruses spread on removable media, particularly floppy | | | | a friend (a trusted source) and follows the link to the |
| disks. In the early days of the personal computer, | | | | website, the virus hosted at the site may be able to |
| many users regularly exchanged information and | | | | infect this new computer and continue propagating. |
| programs on floppies. Some viruses spread by | | | | The newest species of the virus family is the |
| infecting programs stored on these disks, while others | | | | cross-site scripting virus. The virus emerged from |
| installed themselves into the disk boot sector. | | | | research and was academically demonstrated in 2005. |
| Traditional computer viruses emerged in the 1980s, | | | | This virus utilizes cross-site scripting vulnerabilities to |
| driven by the spread of personal computers and the | | | | propagate. Since 2005 there have been multiple |
| resultant increase in BBS and modem use, and | | | | instances of the cross-site scripting viruses in the wild, |
| software sharing. Bulletin board driven software | | | | most notable sites affected have been MySpace and |
| sharing contributed directly to the spread of Trojan | | | | Yahoo. |
| horse programs, and viruses were written to infect | | | | |