YouTube Ordered To Release User Data

Fricklas said Viacom is open to the anonymity request and has consulted with the Electronic Frontier Foundation on possible approaches.

"Any information that we or our outside advisers obtain -- which will not include personally identifiable information -- will be used exclusively for the purpose of proving our case against YouTube and Google, and will be handled subject to a court protective order and in a highly confidential manner," Fricklas said.

But making the records anonymous is not fail-safe. In 2006, an AOL researcher inadvertently posted three months' worth of searches typed in by 650,000 anonymous AOL users. Although their identities were masked -- each user was given a randomly generated unique identification number -- the search terms, which included names, home towns and interests, could be collated and used to identify a person, as an enterprising New York Times reporter showed.

The ruling and the response to it underscores the concerns about data collection and Web surfers' lack of control over the use of their personal data.

Jennifer Urban, a law professor at the University of Southern California, said that even if Viacom does not use the information to sue users, "a future litigant may not keep the information private."

What videos people view, what books they read, have long been considered sensitive information, she said, "intensely personal pieces of information we expect people to be able to keep private."

The lawsuit was paired with a similar suit filed as a class action by a British soccer league that broadcasts soccer matches internationally.

Staff writer Peter Whoriskey contributed to this report.