BadTrans virus bites Windows users hard

BadTrans.B is a variant of a virus which first appeared in April. It usually arrives as an email with either the subject line Re: (name of file attachment) or Re: (the subject line of a previous message thread). The email contains a double attachment and a name made up of a series of elements which “alternate like a fruit machine“, according to Mark Sumner, CTO of MessageLabs.

BadTrans.B uses a known exploit, related to the processing of certain unusual MIME types, in certain versions of Outlook Express 5 so as to launch an attachment automatically. The trick, which was also used by the authors of the Nimda worm, means simply previewing an infected email is enough to get infected. Users who double click on an infected attachment also risk infection.

BadTrans.B uses MAPI to spread and gets target addresses from unread messages in a user’s email client. The worm also drops a file named kdll.dll, which is the password stealing Trojan PWS-AV , on an infected user’s PC.