Symantec Security Response - W32.Jitux.Worm:
"W32.Jitux.Worm is a worm that attempts to spread through MSN Messenger.

This threat is written in the Visual Basic (VB) programming language. The VB runtime libraries are required for it to be executed."

http://securityresponse.symantec.com/avcenter/venc/data/w32.jitux.worm.html