[Skunkworks] Web filters

Hi guys, There is this story in the news that China has demanded PC manufacturers install web filters in all new machines in China or something close to that. Without getting into how good or bad that move is, can someone enlightem me on how that filtering can be achieved? As far as I know the filtering is implimented at software layer. How will pc vendors do it considering the pc can be used to run any of the many OSes and/or their variants?