The system reportedly runs a genuine copy of Mac OS X 10.5 Leopard, and "chris555" has built two such systems, which are available on eBay. Apple has remained silent in regards to Psystar, which is unusual for a company that is typically quick to slap down unofficial products which offer vast similarities to those that it makes. Apple's silence could relate to the perception that refusing to allow an operating system to run on hardware of a user's choice constitutes antitrust behavior. Precedent was set in the matter by the US Circuit Court of Appeals in 1984, while the US Supreme Court allegedly refuses to review the case.