Thời sự

With more than half a billion Chinese online, and many of themavid microbloggers, the speed of censorship uncovered on Sina Weibo is astonishing. The researchers mined data on microblog comments removed by administrators, and found that nearly a third of the deleted posts were taken down in the first 30 minutes.

Unsurprisingly, criticism of the government, local scandals and complaints about China's one-child policy were blocked most quickly. But the team worked out that if none of the process was automated, Sina Weibo would need to employ more than 4,000 speed-reading censors a day, just to keep up.

The researchers uncovered a range of devices aimed at bringing bloggers into line. They included: hiding posts from other users,flagging repeat offenders for closer scrutiny, and tracking backwards to delete sensitive topics everywhere they arose.

With China's media so strictly controlled, the study has raised questions about why microblogs allow people to post before censorship at all. One of the researchers, Professor Dan Wallach, told the BBC that Sina Weibo had to satisfy government censorship requirements without seeming heavy-handed to its bloggers. He said it had to walk a fine line.