A Californian court has cleared a former Intel worker of wrongdoing for using the microchip maker's email to fire off disparaging messages to 35,000 workers at the firm, in a case that tested the boundaries of free speech online.

Intel had accused the man, Kenneth Hamidi, of trespassing on its computer servers, in much the same way that someone could be prosecuted for intruding on private property.

Laws governing the internet are in their infancy and regulations covering the use of email are closely watched. The deluge of spam is forcing governments and software companies worldwide to find ways of stemming the tide.

California supreme court was divided but found in Mr Hamidi's favour four to three.

Justice Kathryn Werdegar, in the majority verdict, said: "He no more invaded Intel's property than does a protester holding a sign or shouting through a megaphone outside corporate headquarters, posting a letter through the mail or telephoning to complain of a corporate practice," she said.

The case should not be taken as a precedent for senders of spam or other unsolicited emails. Trespassing could still be used to prosecute if a mass mailing caused disruption or damage to a company's computer network, she said.

Mr Hamidi, a former engineer at Intel in Silicon Valley, became a thorn in the company's side after he was fired in 1996. He set up an organisation called Former and Current Employees of Intel and began sending out information attacking the company.

Over a 21-month period he sent six mass emails to thousands of Intel employees. Mr Hamidi, who had been prevented from emailing Intel workers by an injunction in place since 1998, vowed to resume his email campaign. "This was a very clear case of people versus corporations and people won," he told the San Francisco Chronicle.

An Intel spokesman said: "We're evaluating the ruling to determine what steps we will take should Mr Hamidi start spamming again."

One of the dissenting justices said the court had effectively condoned an electronic invasion of property.

"Intel should not be helpless in the face of repeated and threatened abuse and contamination of its private computer system," said justice Richard Mosk.