Antivirus companies are warning of a virulent new worm, Sober.C, which spreads by mailing itself to its victim's contacts.
Although the worm was discovered during the weekend, several companies have since upgraded their warnings. Symantec are describing the threat as a "medium level", while Network Associates, the makers of McAfee, upgraded its threat description to medium a short time ago.
Email filtering service operator MessageLabs has also warned of the latest threat, and said it "has intercepted a significant number of copies of… [the virus] during the past 24 hours," the company said. "The first copy of the virus appears to have been sent from Germany, and Sober.C appears to be most active in that region at the moment."
Sober.C uses its own SMTP, or Simple Mail Transfer Protocol, engine to propagate itself. It presents users with fake warnings and errors when it takes control of a system. It arrives with a subject line that may be written in German or English, and the name of its executable attachment varies.