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, according to the latest claims in the ongoing copyright dispute between Apple and Mac clone maker Psystar.

In new allegations, Psystar claims Apple uses so-called stealthware to protect what Psystar claims is an illegal monopoly in the Mac computing market. Specifically, Psystar contends that OS X runs a startup routine that checks whether the host computer is running on Intel dual core processors, which are included in genuine Macs.

Psystar claims that if the OS discovers unapproved hardware, it shuts down. "The check stops the execution of the Mac OS on any computer that is not an Apple-Labeled Computer Hardware System," Psystar states in court papers filed Monday in U.S. District Court in San Francisco.

Psystar maintains that less-expensive chips and hardware are fully capable of running Leopard. The allegations echo charges that Apple has used embedded code to brick iPhones running nonapproved applications.

Psystar sells unauthorized Mac clones from a nondescript warehouse in a Miami industrial park. Apple sued the company earlier this year for copyright violation. Psystar countersued in response, claiming that Apple's control of the Mac market violates antitrust laws.

Last month, a judge rejected Psystar's counterclaim -- leading Psystar to file revised claims on Monday. The new complaint contends that Apple's "leveraging" of its Mac OS copyright to dictate which hardware is allowed to run the OS is beyond the scope of the copyright.

Psystar is now asking the judge overseeing the case to declare Apple's Mac OS copyrights invalid.

For its defense and countersuit, Psystar has retained high-profile Silicon Valley law firm Carr & Ferrell. If Psystar prevails in the case, it could pave the way for mainstream PC makers like Dell, HP, and Lenovo to enter the potentially lucrative Mac market.

In court filings, Apple has said it believes Psystar is backed by a silent third party.