NEW YORK, NY -- A federal judge has ordered YouTube to disclose who watches which video clips and when on the popular video-sharing Web site.

Viacom and other copyright holders have argued that they need the data to show whether their copyright-protected videos are more heavily watched than amateur clips.

Lawyers for Google, which owns YouTube, says producing the data would be expensive, time-consuming and a threat to users' privacy.

The data would not be publicly released but disclosed only to the plaintiffs. And it would include less specific identifiers than a user's real name or e-mail address.

The judge ruled this week that the plaintiffs have a legitimate need for the information and that the privacy concerns are speculative.