New viruses feed on MyDoom infections

Two worms that take advantage of computers whose security has already been compromised started spreading on Monday, antivirus software companies warned. The two opportunistic programs--dubbed Doomjuice and Deadhat--threatened only those users still infected with a version of the MyDoom virus, and didn't pose a major problem for businesses, which had previously cleaned systems infected with the virus, the companies said.

"There are only about 50,000 or 75,000 machines left that are infected," said Vincent Gullotto, vice president for antivirus and vulnerability emergency response team at Network Associates.

Doomjuice, whose spread has been moderate, attempts to direct any re-infected PC to attack Microsoft's Web site, Gullotto said. The re-invigorated attack may be responsible for making Microsoft's site inaccessible late Sunday night and early Monday morning, according to Internet performance measurement firm Netcraft.

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