W32/Mytob-BA is a mass-mailing worm and Trojan with an IRC backdoor. W32/Mytob-BA is capable of spreading through various operating system vulnerabilities such as LSASS (MS04-011).

Emails sent by W32/Mytob-BA have the following characteristics:

Subject line:
Error
Status
Server Report
Mail Transaction Failed
Mail Delivery System
hello
Good day


Message text:
Here are your banks documents.

The original message was included as an attachment.

The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment.

The message contains Unicode characters and has been sent as a binary attachment. Mail transaction failed. Partial message is available.

The attached file consists of a base name followed by one of the extentions BAT, CMD, PIF, SCR, EXE or ZIP. The worm may optionally create double extensions where the first extension is DOC, TXT or HTM and the final extension is PIF, SCR, EXE or ZIP. W32/Mytob-BA harvests email addresses from files on the infected computer and from the Windows address book.

More information can be found at this Sophos page.