It's what different companies call it.
* Win32/Conficker.A (CA) <-
http://www.ca.com/us/anti-virus.aspx* W32.Downadup (Symantec) Norton/Symantec
* W32/Downadup.A (F-Secure) <-
http://www.f-secure.com/en_EMEA/security/* Conficker.A (Panda) <-
http://www.pandasecurity.com/infected_or_not/us/And so on. The same infection may have multiple names. Depends on what scanner you are using.