According to court papers filed last week in US District Court in San Francisco, the clone maker says Apple "is prohibited from bringing action against Psystar for the alleged infringement of one or more of the plaintiff's copyrights for failure to register said copyrights with the copyright office as required," The claim, if true, could undermine Apple's ability to restrict third parties, such as Psystar, from selling clones that run the Mac OS on generic PC hardware.

InformationWeek says it "was not immediately able to verify the claim." Psystar also claims that Apple's Mac OS X 10.5 ("Leopard") operating system contains undocumented code designed to render inoperable personal computers that aren't running on Apple-approved hardware.

Earlier this month Apple added new charges to the federal lawsuit it filed nearly five months ago against a Florida clone maker, claiming that Psystar broke antipiracy defenses that lock Mac OS X to its own hardware.

Apple also said others besides Psystar were involved, but it didn't spell out who. In a filing dated Nov. 26, Apple amended its original suit of July after it had "discovered additional information." Among the additions is a new accusation -- that Psystar violated the Digital Millennium Copyright Act (DMCA) by dodging copy-protection technologies Apple uses to protect Mac OS X, notes Computerworld.

Psystar -- which makes and sells Mac clones -- has claimed in the past that Apple has violated Sherman antitrust rules and other U.S. laws. Psystar claims in court documents filed in U.S. District Court for San Francisco that Apple “has engaged in certain anticompetitive behavior and/or other actions that are in violation of the public policy underlying the federal copyright laws.”

In response, Apple said the defendant, Psystar, “is knowingly infringing Apple’s copyrights and trademarks, and inducing others to do the same.” Psystar makes and sells personal computers that use, without permission, Apple’s proprietary operating system software.