Google announced a while ago that they are going to stop censoring the Chinese version of its search engine. Google threatened to leave the Chinese market.
One of the main reason was the attack on google from Chinese hackers. Google claims that it was directly from China.
The attack, which used a bug in the Microsoft Internet Explorer and not to forget the trojan named Hydraq is considered sophisticated. Because the level of the technical expertise and the information the hackers had was high. They knew exactly who to attack, and where to attack it.