It's From the FBI

The Register reports that the latest variants of the prolific Sober worm series are posing as messages from either FBI or CIA investigators in an attempt to dupe Windows users into opening infectious attachments. The trick was last used in February.

On Tuesday afternoon, variants of the worm had accounted for over 35 per cent of all viruses reported to UK-based security firm Sophos, making it the most prevalent virus currently spreading across the world. The FBI is so concerned about the messages that it has issued a warning on its website. The FBI has urged users who receive the viral emails to report them to the Internet Crime Complaint Centre (ic3.gov).