Microsoft has been found guilty of wilfully infringing another company's patent.
In a lawsuit that dates back to 2003, a Rhode Island jury has ruled in favour of Uniloc and ordered Microsoft to pay $388 million in damages.
The patent in question was for an anti-piracy solution from Uniloc, that makes software "that ensures licensing rights and security".
Microsoft apparently lost its argument that the patent was invalid - because it wasn't.
Microsoft plans to appeal, although they may want to rethink their defence before they do.