Microsoft will not have to pay $388 million to a security software company for infringing on a patent, a US judge has ruled.

Uniloc, which has headquarters in California, had accused Microsoft of infringing a patent related to the antipiracy software-registration system Microsoft uses as part of its product activation.

Microsoft's successful appeal comes after a jury found in April that the company violated Uniloc's patent, which Smith vacated Tuesday.

Microsoft's product-activation procedure links software to particular machines, which is intended to reduce piracy. The applications can be reinstalled repeatedly on the same computer, but not installed on other ones.