It’s been a rough year for nonpracticing entities, with adverse rulings and tough regulations putting the squeeze on what had been a lucrative business. Now they have a new worry: trolls who prey on trolls.

So-called PTAB trolls aim to extract settlements from patent holders by threatening to seek inter partes review, the new procedure that can lead the U.S. Patent and Trademark Office to toss out a patent. Patent holders who’ve won large infringement awards make juicy targets, since a successful IPR could zap their judgments.