The Nimda virus is a malicious file-infecting computer worm. The first released advisory about this threat (worm) was released on September 18, 2001. Nimda 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. However, they also noted that a computer in Canada was responsible for an October 11, 2001 release of infected emails alleging to be from Mikko Hyppönen and Data Fellows (F-Secure's previous name).

Methods of infection

Nimda proved effective partially because it—unlike other infamous malware like Code Red—uses five different infection vectors: