The FBI must continue its search for the culprits in the recent attack on the Internet that resulted in tens of thousands of computers being disabled and millions across the globe experiencing slowdowns.

The worm, variously known as slammer or sapphire, took advantage of a vulnerability in some Microsoft Corp. software that had been discovered in July.

The agency's experts say it won't be easy to track them down. These experts, including many who provide technical advice to the FBI and other U.S. agencies, said exhaustive reviews of the blueprints for the attacking software are yielding few clues to its origin or the author's identity.

"The likelihood of being able to track down the specific source of this is very unlikely," said Ken Dunham, an analyst at iDefense Inc., an online security firm. "We don't have the smoking gun."

But they could be treated as terrorists, even though they didn't attempt to blow up a building.

The worm's author could face up to life in prison under new U.S. anti-terror legislation passed two months ago, some legal experts said. With an increase in online banking and other financial transactions, hackers could do heavy damage despite firewalls set up to protect computers from such attacks.

Under the Cyber-Security Enhancement Act, prosecutors can seek a life sentence against hackers caught launching attacks that cause or attempt to cause deaths. An attack aimed at causing "serious bodily injury" could result in 20 years behind bars.

An FBI spokesman, Paul Bresson, acknowledged the challenges facing cyberinvestigators given the scarcity of clues tucked inside the computer code.

This doesn't mean that investigators won't get lucky. Many hackers want to be famous and want to talk of their exploits.

As a result, hackers routinely draw the FBI's attention by claiming credit for their online exploits in chat rooms. That's how the FBI traced attacks against major American e-commerce sites in February 2000 to a Canadian youth.

The agency must pursue these hackers and send a clear message that tampering with computers is a serious crime with serious consequences.