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“Some of those sites were very high-value,” Mr. Rejaie said.

But the response by some copyright holders has drawn criticism.

Many copyright lawsuits are “quite legitimate,” said Rebecca Jeschke, media relations director for the Electronic Frontier Foundation, an Internet rights group based in San Francisco.

But she told The Times in an e-mail that a recent series of “mass infringement cases, where hundreds or even thousands of plaintiffs are lumped together” were “deeply flawed.”

In one case filed last week, for instance, Delaware-incorporated XPays, Inc., which owns the copyright to the Paris Hilton sex tape, is seeking damages against 843 “John Does” — BitTorrent users identified only by the Internet addresses from which they logged onto the service.

Ms. Jeschke called such efforts “copyright trolling,” saying companies were trying “to grow businesses out of suing Internet users … exploiting the massive damages in copyright law in order to pressure defendants into settling quickly.”