Stanton decided Viacom needed more than user log-in names and IP addresses to target unique YouTube visitors. Nonetheless, privacy advocates are calling the ruling a blow to online privacy.

Some are criticizing Viacom for making the discovery request. Marc Rotenberg, executive director of the Electronic Privacy Information Center (EPIC), doesn't entirely disagree with those concerns, but he said the larger issue is Google's business practices.

"Viacom is doing what an aggressive corporation does when it files a lawsuit, which is to try to learn as much as it can about whether its rights have been violated," Rotenberg said. "Google, because it's sitting on all this information , is making it much easier for Viacom to pursue litigation."

The IP Address Connection

While the court denied Viacom's request that YouTube turn over the source code that powers its search engine, Stanton did require YouTube to hand over information that records all video viewing for the site. That data shows which users watched which videos and when.

"The logging database does not identify users by name, but it does contain users' IP addresses and unique log-in IDs. A log-in ID will be whatever the user chose -- which could be anything from a nonsensical set of characters or a random word to the user's actual name," wrote Dave Sohn, senior policy counsel for the Center for Democracy and Technology.

Sohn figures that in a substantial number of cases, the ID will contain name or e-mail information. In those cases, the ID, perhaps aided by the IP address, could be sufficient to determine the real-world identity of the user. So the logging database will include identifying information for such individuals and their full YouTube video-viewing history, Sohn suggested.

Google's Stand Used Against It

When the issue of IP addresses and privacy came up last year in the wake of a Department of Justice subpoena, which Google opposed, EPIC warned that Google's data-retention policies could cause user information to become a target of future law-enforcement and discovery requests -- and that's exactly what happened, Rotenberg said.

"Our other big objection, of course, is that Google didn't take seriously the fact that IP addresses are personally identifiable. We've made this argument repeatedly over the past couple of years," he continued. "Google dismissed it and even wrote a blog posting in February of this year saying IP addresses aren't personally identifiable."

When the judge ruled against Google, he found the company's blog entry that Rotenberg referenced. In an effort to block Viacom's request for YouTube's data, Google claimed a privacy interest in revealing the IP address. But the judge cited Google's corporate blog post stating IP addresses don't represent a privacy interest and ruled in Viacom's favor.

"It's very ironic, but it's also somewhat tragic. If Google had done the right thing earlier -- if Google hadn't retained so much data, but instead admitted that IP addresses, particularly when joined with other types of data such as search queries, dates and times, makes it pretty easy to identify Internet users -- Viacom might not have won its request for YouTube data," Rotenberg said.

Google could not immediately be reached for comment. Viacom issued a statement last week saying it will handle YouTube information confidentially.