The Nimda virus is a malicious file-infecting computer worm that quickly spread, surpassing the economic damage caused by previous outbreaks.
It was released on September 18, 2001, one week after the attacks on the World Trade Center and Pentagon. It affected both user workstations (clients) running Windows 95, 98, NT, 2000, or XP and servers running Windows NT and 2000.
The worm's name comes from the reversed spelling of "admin". F-Secure found the text "Concept Virus(CV) V.5, Copyright(C)2001 R.P.China" in the Nimda code, suggesting its country of origin. A computer in Canada was responsible for an October 11, 2001 release of infected emails alleging to be from Mikko Hyppönen and Data Fellows.