Nebraska attorney general Jon Bruning suffered a legal setback Monday. A federal judge ruled that Bruning violated the constitutional rights of a law firm's client when he sent a cease and desist letter to the firm demanding that it cease patent infringement efforts in Nebraska. But the attorney general pledged to continue his investigation of patent trolls in the state, and to take further legal action if the investigation uncovers evidence of misconduct.

Bruning launched his fight against patent trolls this summer. He believes that troll tactics run afoul of Nebraska consumer protection law. In July, he sent the law firm of Farney Daniels a letter demanding that it turn over information about its patent enforcement efforts in Nebraska. And he ordered the firm not to launch any new patent enforcement efforts in the state until after he had completed his investigation.

Farney Daniels sued, arguing that the enforcement ban violated the rights of one of its clients, flat panel display vendor Activision TV, to enforce its patent rights. On Monday, Judge Joseph F. Bataillon sided with Activision.

"Activision's First Amendment rights are being violated, and it is questionable whether the Attorney General has the right to maintain the cease and desist order given the preemption in this area of law," Bataillon wrote. "Activision's constitutional right to hire counsel of its choosing and pursue investigations and lawsuits against infringers is clearly impeded by the cease and desist order."

But Bruning says the ruling won't stop his investigation of troll tactics. "Nothing in the judge’s order stops our ongoing investigation into patent trolls and law firms that represent them, specifically Farney Daniels," Bruning said in a Tuesday statement. "This is a limited issue that has no bearing on our patent troll investigation going forward. We will continue to work with other states to investigate the baseless harassment perpetrated by patent trolls."

This year, attorneys general in Minnesota and Vermont have also taken action to try to curb patent trolling in their states.