And when officials demand that tweets disappear, they don't necessarily take "no" for an answer. When human rights campaigner Wang Aizhong refused to delete his tweets, someone hijacked his account and deleted 3,000 of his messages. While there's no confirmation of who was responsible, Wang put the blame on government-linked hackers who insisted on silencing him.

The likely aim, as you might imagine, is to maintain the ruling party's authority and control the country's image. China is happy to use Twitter and other foreign social networks to promote its official point of view, but doesn't want its residents to challenge that view on those same networks. And unfortunately, that makes life even more difficult for activists who may lose access to one of their few remaining public outlets.