[timinman]

This was brought on by an unforeseen natural evolution of antivirus software.

1. The software becomes sentient, learns to define, recognize and delete viruses on it's own.

2. The software realizes that by every definition it is itself a virus and must delete itself. :)

[dhimes]

1.5 The software decides that Man is a virus and must be eliminated.

[chimeracoder]

1.25: The software gets distracted by its own self-awareness. Crisis averted. (http://xkcd.com/1046/)

[duiker101]

We all know that in the end the "bug" is always between the chair and the keyboard.