I have an aunt in china, and my father travels a lot, sometimes he goes to china. When he was in China last, he was visiting my aunt, and they had one of those 'moments' where they discover how sophisticated the censorship in China is.

My father had the BBC website open in his web browser. My aunts computer was next to it, and she opened the BBC website, and they noticed that on my aunts computer, there were gaps where news stories should have been. On my fathers computer, they contained little snippets of headlines, photos, etc. These stories were 'snipped' out of the HTML on my aunts computer.

They were obviously quite confused, as they were accessing the internet over the same internet connection, until my father realised that he was using a VPN into an office in Australia. So all his web traffic was going over an encrypted tunnel to Australia, where it was getting uncensored full access to the internet, while my Aunt was getting the Chinese version of the internet, which from the evidence visible, was either getting modified before being transmitted from the BBC servers, or being censored on its way into china via some kind of transparent content modifying proxy.

Not only does China censor the internet. They've got advanced methods for doing it.