SAN FRANCISCO (MarketWatch) -- It's no secret that millions of Internet users every day watch copyright-infringing video clips on YouTube, the upstart Web site that Google Inc. has agreed to acquire for $1.65 billion.

What's less known is that YouTube has been watching the watchers.

YouTube's actions in response to a subpoena it received in May show that it has been keeping tabs on users who post copyrighted material to its site -- and in one case shared the name of a user with lawyers from a Hollywood film studio.

On May 24, lawyers for Viacom Inc.'s Paramount Pictures convinced a federal judge in San Francisco to issue a subpoena requiring YouTube to turn over details about a user who uploaded dialog from the movie studio's "Twin Towers," according to a copy of the document.

“ 'I was happy to utilize YouTube when it was still not clearly established. It felt a bit utopian, even though the days for that were clearly numbered.' ” — Chris Moukarbel, filmmaker

YouTube promptly handed over the data to Paramount, which on June 16 sued the creator of the 12-minute clip, New York City-based filmmaker Chris Moukarbel, for copyright infringement, in federal court in Washington.

That YouTube chose to turn over the data, rather than simply remove the offending video from its site -- as it did Friday when it agreed to take down 30,000 videos at the request of a group of Japanese media companies -- came as a surprise to copyright experts.

"YouTube seems to have given up too easily," said Laurence P. Colton, an intellectual-property lawyer at the firm of Powell & Goldstein LLP in Atlanta.

Its prompt legal capitulation suggests that YouTube users who post copyrighted material should not expect the company to protect them from media-business lawsuits, said Colton, whose firm wasn't involved in the Paramount subpoena or lawsuit and who learned of them from a MarketWatch reporter.

The "Twin Towers" episode is reminiscent of the way the entertainment industry vanquished the first version of Napster Inc. NAPS and other digital-music sites that made it easy to download copyrighted songs over the Internet.

Music company lawyers first warned and then sued individual users who downloaded their songs. Now it looks like piracy hunters for the movie studios are using the same technique against YouTube users.

YouTube's decision to help Paramount track down Moukarbel stands in stark contrast to the philosophy of Google, which has fought the U.S. Justice Department over attempts to access data about consumers who use its search services.

Google GOOG, +0.13% has balked at releasing even the most innocuous information about its users' behavior to the U.S. government in the past. Also, it's now battling requests for user details coming from Brazilian and Indian government investigators.

Google declined repeated phone and e-mail requests for comment for this story. Julie Supan, YouTube's senior marketing director, declined comment.

The end of 'utopia'

With more media companies signaling that they will come after YouTube for compensation over copyrighted material, Moukarbel's experience suggests that some of those among the Web site's 40 million users who post copyrighted material can expect legal trouble.

Moukarbel settled the suit after he admitted making the film and agreed to remove it from his own Web site and from YouTube, according to a copy of a court order that was part of the settlement. He also agreed to make an effort to remove it from other sites where it had been posted.

Moukarbel told MarketWatch in an interview that YouTube's actions signaled to him the end of an era for the video site.

"I was happy to utilize YouTube when it was still not clearly established. It felt a bit utopian, even though the days for that were clearly numbered," Moukarbel said.

It remains to be seen if this has any chilling effect on the phenomenal growth of YouTube, which was founded just 20 months ago by former executives of PayPal, the electronic payment firm that was eventually acquired by eBay Inc.

The freewheeling nature of the site - and its apparent cloak of user anonymity -- has helped the upstart become a top 20 Web site whose users watch up to 100 million video clips every day.

A slew of lawsuits like those filed against individual digital music pirates could change that atmosphere, and perhaps the growth rate, of YouTube's online community.

"This community was built as a kind of free-for-all, where people could have a lot of fun and do it rather anonymously," Colton said. "You don't get that kind of community by saying, 'Here, sign up and at the simplest drop of a subpoena, we'll give that information away.' "

To be sure, Google, which hopes to close the YouTube purchase by year's end, has already taken steps to reduce the copyright liability it will inherit from the private firm. Just before it announced the acquisition of YouTube, the two companies signed licensing agreements with several large media firms, including Vivendi's Universal Music Group, Warner Music Group Corp. WMG, +0.67% , Sony BMG and CBS Corp. CBS, -4.76%

Several large entertainment industry providers are now teaming up to request compensation from the site, according to The Wall Street Journal. Viacom VIA, -9.09% , which owns Paramount, estimates that pirated versions of video clips from its MTV, Comedy Central and Nickelodeon channels are watched 80,000 times a day on YouTube, according to the Journal.

Paramount Pictures spokeswoman Nancy Kirkpatrick said that the company's actions against Moukarbel "in no way means we're targeting YouTube." She declined further comment on the lawsuit against Moukarbel.

When asked about YouTube, a spokeswoman for the Motion Picture Industry Association said "we continue to pursue those who violate copyright laws on all levels, and we will continue to monitor YouTube for copyrighted material."

That means YouTube users who post such material could face legal problems similar to Moukarbel's.

Moukarbel, meanwhile, said he harbors no hard feelings toward YouTube about the incident.

"I was happy with its run on YouTube, and, frankly, I was surprised it lasted as long as it did," he said. "That they eventually offered my information to Paramount doesn't bother me at this point."