Computer equipment at two Californian universities have been found to have played a part in this week's crippling cyber assault on leading commercial internet sites.

A desktop computer at the University of California was used for the attack on CNN, while Ebay was hit by data transmitted in part from an internet router at Stanford University.

Kevin Schmidt, network programmer at the University of California's Santa Barbara campus, said he had discovered an abnormality in the university's computer traffic on Tuesday night which had alerted him to the assault on CNN.

He said a desktop computer in a research lab had been electronically broken into by a hacker sometime before the attack.

Mr Schmidt said that there was no indication anyone in the university had been responsible. He is now assisting the FBI in trying to locate the origin of the attack.

A university spokesman confirmed that a flood of hacker messages had been sent to CNN's site via one of the servers at the campus.

CNN itself reported on Friday that the FBI was "zeroing in on undisclosed locations in California and Oregon" in its effort to track down from where the attacks originated.

Security probe

The focus of the FBI investigation has shifted from the target sites to secondary "zombie" sites - such as the one at Santa Barbara - from where the intruders staged their sabotage.

But FBI spokeswoman Debbie Weierman said no search or arrest warrants had yet been issued.

"We are following all leads aggressively. We are interviewing representatives of the victim companies and gathering information and data."

The Pentagon said earlier that it would check nearly 10,000 of its computer networks to make sure none was used in the attacks.

For his part, President Bill Clinton has called government officials and computer security experts to a meeting next week to discuss how to prevent a repeat of the attacks, which it is feared could undermine confidence in e-commerce.

He said there were no instant solutions to the problem, but pledged that the authorities were doing all they could.