Carries out an action against the targeted computer system—such as taking it offline, as in Denial of Service (DoS). An active attack could also be made to target information by altering it in some way—as in the defacement of a Website. A passive computer attack, in contrast, simply eavesdrops on or monitors targeted information but does not alter it.
Graham, R. Hacking Lexicon. [Online, 2001.] Robert Graham Website. http://www.linuxsecurity.com/resource_files/documentation/hacking-dict.html.