[ccrush]

Clean room reverse engineering. The idea that, if you build something with a specified interface (Windows API in this case) without prior knowledge of the implementation details, and you haven't broken any patents in doing so, then you haven't broken copyright either and you are free to do business. This is a gross oversimplification. See Intel vs AMD case for more details.

[yoklov]

Clean room is a defense against copyright and not patent, AIUI. For patents it doesn't matter if you knew someone had patented it.

Not a lawyer, though, but a quick search confirms this.