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The disbanded Prenda Law firm, once denounced by a judge as a “porno-trolling collective,” committed discovery abuses and could face sanctions for additional misconduct, the U.S. Court of Appeals for the D.C. Circuit ruled on Tuesday.

The appeals court struck down a lower court order directing Internet service providers to hand over information about unnamed defendants facing copyright infringement claims brought by Prenda. Judge David Tatel, writing for a three-judge D.C. Circuit panel, said Prenda made no effort to limit its requests to individuals with ties to Washington.

Some of the subpoenas went to Internet service companies who don’t provide service in the District, Tatel wrote. And in subpoenas to companies that do operate in D.C., he said, Prenda didn’t take even the most basic steps to narrow the request to local users.

“[S]ometimes individuals seek to manipulate judicial procedures to serve their own improper ends,” Tatel wrote. “This case calls upon us to evaluate—and put a stop to—one litigant’s attempt to do just that.”

Prenda represented AF Holdings LLC, a company created by Prenda lawyers that held copyrights to adult films, according to court papers. Prenda filed lawsuits across the country against unnamed defendants who allegedly illegally downloaded those films. The firm would subpoena service providers for information about the users, and then attempt to negotiate settlements with those individuals. Critics accused Prenda of being copyright trolls and abusing the court system.

Prenda’s Paul Duffy, who argued for AF Holdings, did not immediately return a request for comment. According to news reports Tatel cited, Prenda no longer exists, but the firm was “reconstituted in a similar form.”

Benjamin Fox of Morrison & Foerster argued for the Internet service providers—Cox Communications Inc., Verizon Online LLC, Bright House Networks LLC, AT&T Internet Services and Comcast Cable Communications Management LLC. He could not be reached for comment on Tuesday morning.

The ruling strikes a blow to all copyright trolls, not just Prenda, said Corynne McSherry, a lawyer with the Electronic Frontier Foundation who argued in support of the Internet service providers. McSherry said it was the first time a federal appeals court struck down “the legal linchpins of the copyright troll business model”—suing hundreds of defendants together without any reason to believe they fell within the court’s jurisdiction.

“We had plenty of district courts come to similar decisions, but now we have a very clear, very firm decision from an appellate court,” she said.

Tatel said plaintiffs seeking the type of information AF Holdings wanted about unnamed defendants must have “at least a good-faith belief” discovery would prove the court had jurisdiction.

“Here, we think it quite obvious that AF Holdings could not possibly have had a good-faith belief that it could successfully sue the overwhelming majority of the 1,058 John Doe defendants in this district,” he wrote.

The court also ruled that AF Holdings couldn’t join defendants in a single lawsuit solely because they downloaded a film from the same source via online file-sharing service BitTorrent.

“To paraphrase an analogy offered by amicus counsel at oral argument,” Tatel wrote, “two BitTorrent users who download the same file months apart are like two individuals who play at the same blackjack table at different times.”

Tatel added that other courts found AF Holdings based its copyright claims on a document bearing at least one forged signature. He said that issue didn’t affect the appeals court’s ruling, but that the trial judge could decide whether sanctions were called for.

Senior judges Laurence Silberman and David Sentelle also heard the case.

Contact Zoe Tillman at ztillman@alm.com. On Twitter: @zoetillman.