A computer virus (that computer virus; Plural: the computer viruses) is itself an increasing computer program, which transfers itself into other computer programs and itself thereby reproduced. The classification as a virus refers here to the spreading and infection function.

Once started, it does not know controllable changes in the status of the hardware (for example network connections) of the user, at the operating system or at the software makes (harming function). Computer viruses can impair and rank through from the creator wished or desired functions computer security among the mark commodity.

The expression computer virus is used also falsely for computer worms and Trojan horses, since the transition is to be recognized in the meantime flowing and for users often not.