BadTrans virus bites Windows users hard

Computer users turned on their PCs this morning to find their In-boxes flooded with copies of the latest mass mailing virus.

BadTrans.B is spreading rapidly after infecting a large number of home users in the UK over the weekend. BTOpenworld shut off an email system today, but not before infecting many customers with the virus.

MessageLabs, a managed services firm which scans for and blocks viruses in email for clients, has blocked 5,164 copies of the virus this morning. Its figures show btinternet.com, ntlworld.com and freeserve.co.uk as the most common sources of the virus.

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.

Users should update their antivirus protection to guard against the virus. In addition, corporate users should consider blocking emails with .pif or .scr attachments at the email gateway, a step that would block BadTrans.B before it reaches user's desktops. ®

External links

Good analysis of the virus outbreak by MessageLabs
Description of the BadTrans-B worm by Sophos
Incorrect MIME Header Can Cause IE to Execute E-mail Attachment (MS bulletin and links to a patch)

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