Nimda

Nimda is a computer worm, and is also a file infector. It quickly spread, eclipsing the economic damage caused by past outbreaks such as Code Red. Multiple propagation vectors allowed Nimda to become the Internet’s most widespread virus/worm within 22 minutes. Nimda affected both user workstations (clients) running Windows 95, 98, Me, NT, 2000 or XP and servers running Windows NT and 2000. The worm's name spelled backwards is "admin".