Google has successfully overturned a judgment which would have compelled it to release the personal details of YouTube users as part of a legal action that is being brought against the site.

The search giant said it had reached an agreement with Viacom, the entertainment giant which is suing YouTube for $1 billion, which will protect the privacy of YouTube users whose details have been requested by Viacom in its copyright infringement case.

Viacom, the parent company of MTV, had asked Google to hand over information about YouTube users, including their user names and their IP addresses - the number that identifies every device that is connected to the internet - as part of its case which alleges that YouTube has hosted vast quantities of illegally uploaded content.

Earlier this month, a district court judge in New York ordered Google, which owns YouTube, to comply with Viacom's request.

Today, Google said it had come to an agreement with Viacom and other plaintiffs, including the Football Association, which will mean that it still hands over information about how YouTube has been used, but not in a way which identifies individual users.

“We have reached agreement with Viacom and the class action group - they have agreed to let us anonymize YouTube users data," a Google spokesman said. Privacy activists had argued that the court order threatened to expose "deeply private" information, and would have violated privacy legislation.

Viacom had said it needed the information to demonstrate how copyright material had been illegally uploaded to the site and had no interest in identifying individual users.

Using the anonymous information provided by Google, Viacom will now be able to track how an individual computer has interacted with YouTube without knowing the identity of the person who used the computer.

An individual YouTube user's identity can in theory only be ascertained by matching the IP address of their computer, which will be known to YouTube, with the address of the person to whom the IP address is registered, which would typically be known by their ISP.

Viacom's case against Google, which is being run in conjunction with a separate class action filed by the Premier League and several music publishers, is unlikely to go to court until next year or 2010.

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