The People's Republic of China is taking some official steps to exert more control over the use of social media and microblogging services (like Twitter), in advance of a critical Communist Party Congress next year. In the wake of a series of major scandals, it's anticipated that the Congress will be used to announce significant changes in party and political leadership Chinese authorities traditionally try to keep such machinations behind the scenes, and are worried that these services might become a source of unfiltered reporting and speculation, or inconveniently timed reporting of new scandals..
Weibo,the largest microblogging site in China with over 200 million users, has already emerged as a freewheeling forum for breaking news, exposés and edgy opinion — often to the chagrin of censors. For now, the pressure consists of leading politicians and regulators making official statements warning Internet users to “show self discipline and refrain from spreading rumors" and that the "Internet should not be used to jeopardize the national or public interest."
That's sufficient threat for Weibo hosts like Sina to start removing "unsubstantiated rumours" from the system, and blocking accounts of users who post or share them. Sina also announced that it would “put more effort into attacking all kinds of rumors.”
Source - China moves to rein in microblogs, Washington Post