SAN FRANCISCO -- The U.S. Federal Bureau of Investigation today warned computer users not to open a widely circulating e-mail that falsely claims to have been sent by U.S. authorities. The e-mail attempts to trick users into installing a variant of the Sober worm by telling them that they have been spotted on "illegal Web sites," and asking them to click on an attached "list of questions."
"These e-mails did not come from the FBI," the FBI announced in a posted statement. "Recipients of this or similar solicitations should know that the FBI does not engage in the practice of sending unsolicited e-mails to the public in this manner."
A Significant Portion of Global E-Mail
This latest worm now accounts for more than 65 percent of all malicious software being reported to antivirus vendor Sophos, and it constitutes about one in every 74 e-mail messages being sent on the Internet, according to Graham Cluley, a senior technology consultant with Sophos. "It's quite a significant event," he said. "I'm not sure that it's necessarily going to last, but at the moment it's well ahead of any other virus."
Once launched, Sober scans the user's hard drive for e-mail addresses and sends the bogus e-mail to new recipients. After that, it awaits further instructions from its creator, effectively transforming the infected system into a remote-controlled zombie computer that can be used for further spamming or computer attacks.
In some instances, the worm pretends to come from the U.S. Central Intelligence Agency (CIA) or the German police, Cluley said.
Similar to Earlier Variants
Variations of the Sober worm have been circulating for about two years now, and their code is sufficiently similar that they are all thought to have been written by one person, or perhaps by a small group of people, Cluley said.
By mentioning U.S. law enforcement, the worm writers have made it more likely that users will inadvertently launch malicious code, but they may also be goading the FBI and the CIA, Cluley said. "It seems a bizarre thing for the virus writer to do, to pick a fight with the FBI and CIA in this way."
The FBI is taking the matter "seriously," and is investigating, the agency's statement said.