The U.S. Court of Appeals for the Federal Circuit moved to further tighten up Patent Trial and Appeal Board rules on real parties in interest Friday.

The appellate court ruled that the PTAB is making it too difficult for patent owners to prove that third parties are improperly participating in administrative challenges to patent validity.

It's a hot-button issue for patent owners, who say challengers often use business partners or other organizations as cut-outs to skirt the one-year statute of limitations for filing petitions for inter partes review.

Following July's Applications in Internet Time v. RPX, Friday's opinion in Worlds v. Bungie is the Federal Circuit's second ruling this summer tightening real party rules. It involves a dispute over patents on the computer-generated display of avatars in a virtual world.

Nonpracticing entity Worlds Inc. sued Activision Publishing Inc. in the District of Massachusetts in 2012, saying games like Worlds of Warcraft infringe its patents. Worlds notified Activision in 2014 that it intended to add Bungie, an independent video game developer whose game Destiny is distributed by Activision.

Six months later, Bungie filed six IPR petitions challenging Worlds' patents. Worlds argued that Activision was a real party in interest with Bungie, and therefore the IPRs had been filed two years too late. The PTAB ruled that, as IPR petitioner, Bungie enjoyed a rebuttable presumption that it was the sole real party, and that Worlds hadn't presented enough evidence to overcome it.

The Federal Circuit ruled that the PTAB was setting too high a bar.

“We see no particular need to create a formal presumption—especially a presumption that would disfavor the party that likely has inferior access to potential sources of proof,” Chief Judge Sharon Prost wrote for a unanimous panel.

A patent owner must produce “some evidence that tends to show that a particular third party should be named a real party in interest,” she wrote, and Worlds' presented “more than enough evidence to sufficiently put this issue into dispute.” Specifically, she pointed to a software publishing and development agreement that contained indemnification agreements and gave Activision the power to review and clear IP rights involving Bungie's products.

Bungie's attorneys had argued that those IP rights involved only trademarks and copyright. Prost wrote that the PTAB accepted that representation without any evidence. “This implies that the Board assumed the burden of persuasion rests with the patent owner,” she wrote.

The court remanded with instructions to weigh the evidence “in a manner consistent with our recent precedent,” including the Applications in Internet Time decision.

Wayne Helge of Davidson Berquist Jackson + Gowdey had the winning argument for Worlds.

Michael Rosato of Wilson Sonsini Goodrich & Rosati argued for Bungie that Worlds never actually added Bungie to its litigation against Activision. “It has nothing to do with Bungie,” he told the court at the March argument. “It never had anything to do with Bungie.”