In July of 2008 Apple sued a small Florida-based company called Psystar for copyright infringement. Psystar was the maker of so-called Hackintosh systems, non-Apple computers with OSX pre-installed, which is against Apple’s user license for OSX. Psystar countersued claiming, among other things, copyright misuse.
The two sides engaged in a very bitter lawsuit (technically two lawsuits as there was a separate one for OSX Snow Leopard and Leopard) but the tide quickly turned against Psystar as temporary restraining order barred Psystar from selling its clones and that order was, in turn, recently made permanent.
Psystar and Apple did partially settle their differences but there are question surrounding Psystar’s latest product, Rebel EFI, which allows home users to install OSX on Psystar machines.
Apple hasn’t taken a real stance on this program yet, but other clone makers use a similar process without any intervention from Apple.