More than 1 million computers - possibly yours, too - are used by hackers as remote-controlled robots to crash online systems, accept spam and steal users' personal information, the FBI says.

The government has no way to track down all the computers, both in the U.S. and elsewhere, that hackers have massed into centrally controlled collections known as "botnets."

But the FBI has pulled the plug on several botnet hackers, or zombies. One man was charged this week in a scheme that froze computer systems at Chicago-area hospitals in 2006 and delayed medical services.

What was viewed seven years ago as a kind of prank to boot people off-line has evolved into schemes to defraud people by stealing credit card and Social Security data, by crashing retail Web sites and through "pump-and-dump" online stock deals.

In those stock cases, hackers break into online trading accounts to buy and sell stocks, pumping up the price of those they can liquidate and then dumping them.

FBI Deputy Assistant Director Shawn Henry said in an interview Wednesday, "There will likely be spam sent on the heels of this case," people portraying themselves to be from the FBI or saying, 'We're investigating the big botnet case that you heard about and we need to check your computer. Provide us this information.'

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