A US court has ruled in favour of Apple at the close of a long-running legal battle with Mac clone maker Psystar.

Psystar was accused of violating Apple's copyright when it installed the Mac OS X operating system on Intel-based computers.

Apple took Psystar to court 18 months ago, accusing the manufacturer of infringing its copyright and breaking the Digital Millennium Copyright Act.

"Mac OS X on both Mac computers and the DVD are covered by software licence agreements that provide that the software is 'licensed, not sold, to [the user] by Apple Inc'," Apple said in court documents.

"Apple's licence agreements restricted the use of Mac OS X to Apple computers, and specifically prohibited customers from installing the operating system on non-Apple computers.

"In brief, customers were contractually precluded from utilising Mac OS X on any computer hardware system that was not an Apple computer system."

Psystar had been selling PCs with Apple's Snow Leopard pre-installed, along with software tools that let users run Mac OS on any machine.

However, a US District Court judge ruled that Psystar had infringed Apple's exclusive right to create derivative works of Mac OS X by replacing original files in Mac OS X with unauthorised software files.

"Specifically, it made three modifications: (1) replacing the Mac OS X bootloader with a different bootloader to enable an unauthorised copy of Mac OS X to run on Psystar's computers; (2) disabling and removing Apple kernel extension files; and (3) adding non-Apple kernel extensions," the judge said.

A hearing to determine the 'remedies' for the case will take place on 14 December.