A US judge has ordered Google to give Viacom user data used YouTube in a decision condemned by the Google and privacy advocates.

US District Court Judge Louis Stanton backed Viacom's request for data on which YouTube users watch which videos on the website in order to support its case in a billion-dollar copyright lawsuit against Google.

Viacom charges Google, which bought YouTube in 2006, acts as a willing accomplice to Internet users who put clips of Viacom's copyrighted television programs on the popular video-sharing website.

The judge brushed aside privacy concerns on Tuesday while ordering Google to give Viacom log-in names of YouTube users and Internet protocol addresses identifying which computers they used for viewing videos.

Privacy activists from the Electronic Frontier Foundation said in a blog post the order "threatens to expose deeply private information" and violated the Video Privacy Protection Act, a 1988 federal law passed after Supreme Court nominee Robert Bork's video rental habits were revealed.

Viacom issued a statement Thursday saying it is only out to bolster its case against Google and not to expose or pursue viewers of copyrighted videos.

"Any information that we or our outside advisors obtain will be used exclusively for the purpose of proving our case against YouTube and Google," Viacom said.

"It will be handled subject to a court protective order and in a highly confidential manner."

In what Google claims as a partial victory, Stanton denied Viacom's request to get its hands on secret source code used in YouTube video searches as well as for Internet searches.