Researchers say tens of thousands of computers have been hit by a virus-like infection.
It is causing computers to mysteriously restart and launch an electronic attack against a Microsoft Web site.
A message hidden inside the infection appears to taunt Microsoft Chairman Bill Gates, asking, "why do you make this possible? Stop making money and fix your software."
Security experts say the infection, which exploits an unusually dangerous flaw in Windows software, isn't seriously disrupting Internet traffic but poses that risk as it spreads.
Government and industry experts have anticipated such an outbreak since July 16th, when Microsoft acknowledged the flaw affected nearly all versions of its Windows operating system software.