The Chinese government's fondness for restricting access to online services is well documented, but according to a report by researchers at Carnegie Mellon University's Language Technology Institute, even those sites that remain online could be facing the heavy hand of censorship. Using the popular microblogging site Sina Weibo as a test case — the site boasts a userbase larger than Twitter's, and recently smashed Twitter's microblogging speed record — the researchers studied some 57 million messages between June and September of last year. Three months later they checked back on both a random subset of the messages as well as a selection that they deemed politically charged, and found that more than 16 percent of the checked messages had been deleted. 54 percent of those originating from Tibet had also been wiped from the service.

It's not clear who is responsible for deleting the messages, but China has had no qualms about clamping down on social media platforms in the past, blocking both Facebook and Twitter starting in 2009. "What they hope to do is to try to prevent massive organizations of people and problems they saw in the Middle East over the years through social media," said David Bamman, a PhD candidate at CMU. "By preventing people from discussing certain things in China, they have a way to effectively suppress that." The full study, entitled "Censorship and Deletion Practices in Chinese Social Media," will be published in this month's edition of the journal First Monday.