Computer viruses are small programs or scripts that can negatively affect the health of your computer. These malicious programs can create files, move files, erase files, consume your computer's memory, and cause your computer not to function correctly. Some viruses can duplicate themselves, attach themselves to programs, and travel across networks. In fact opening an infected e-mail attachment is the most common way to get a virus.
Tech Terms Dictionary 2014. Per Christensson. 28 February 2014. <http://www.techterms.com>