Antivirus software companies warned customers about a new variant of the Sober e-mail worm, which has begun spreading on the Internet this week masquerading as a Microsoft software update.
It is common for worm authors to dress up their creations as Microsoft software updates. Recent worms including "Swen" and "Gruel" have posed as official correspondence from Microsoft.
In response, Microsoft publicly declared that it never distributes software updates using e-mail. It has published guidelines for identifying legitimate e-mail from the company.
Antivirus companies have posted software updates to detect the new worm. They recommend that customers update their software as soon as possible to prevent Sober.D infection.
Sober's Strategy
Sober.D is the latest version of a worm that first appeared in October. The new version poses as a software patch that will remove the MyDoom virus from infected Windows systems, say representatives of antivirus company F-Secure of Helsinki, Finland.
F-Secure first detected the new worm variant in Germany early Monday. The company rates the virus a "Level 2" threat, indicating "large infections."
Like its predecessors, Sober.D spreads by skimming e-mail addresses from victims' computers, then mailing copies of itself to those addresses. Sober.D also adapts its message for German-speaking audiences, inserting a German-language version of its pitch message into e-mail addresses belonging to German domains, such as those ending in .de, according to F-Secure.
Copies of the Sober.D worm arrive in e-mail messages with the subject "Microsoft Alert: Please Read!" or "Microsoft Alarm: Bitte Lesen!" says the antivirus company. The worm file is embedded in file attachments with the .exe or .zip file extension and with names such as "Patch," "MS-Security," or "UpDate."
Once the worm file has been opened, the virus places a copy of itself on the infected machine's hard drive and modifies the Windows configuration so that the worm file launches each time Windows starts, antivirus companies say.
When run, the worm mimics a legitimate software patch, displaying a pop-up message indicating that the 'patch has been successfully installed'. For machines that are already infected, the worm displays a message saying that the 'patch does not need to be installed on this system', F-Secure says.
