How China censors its social networks

The way the Chinese government censors and deletes politically-sensitive terms online has been revealed for the first time.

As expected, the communists are hypersensitive to criticism of the state - but also to people slating the so-called 'Great Firewall', the network blocking technology that prevents Chinese people browsing the internet freely.

The US study also shows Beijing's censorship machine works in real time - and can adapt quickly to emerging issues. It's also location-dependent, being far more active, when required, in dissident regions.

David Bamman, a computer scientist and linguist at Carnegie Mellon University in Pittsburgh, got the idea for the research last summer when he noticed how quickly false rumours of the death of former Chinese president Jiang Zemin disappeared from China's Twitter equivalent Sina Weibo.

"I went to check back on some of those messages and it really shocked me to discover that around 70 per cent of them had been deleted," Bamman told New Scientist. So with colleagues Noah Smith and Brendan O'Connor he decided to study the censorship mechanism more closely.

They took advantage of the fact that Sina Weibo , China's biggest commercial microblogging network, publishes an interface to encourage developers worldwide to devise smartphone apps that allow Chinese-speaking people anywhere to read and post Twitter-style 140-character messages.

This interface allowed the Carnegie team to download nearly 57 million messages from Sina Weibo between 27 June and 30 September. Once they had these, they then examined Sina Weibo's archive to see which were later deleted. "We could then see which terms in a message meant it had a higher chance of being deleted," says Bammam.

As might be expected, criticism of state propaganda was not tolerated. Messages attacking China's "Ministry of Truth" were zapped, as were ones involving calls for the "resignations" of incompetent government officials, such as that of the railways minister after a horrific train crash . Complaints about Fang Binxing - architect of the web censoring Golden Shield Project, nicknamed the Great Firewall - were also highly deleted - as were mentions of a pair of Communist Party meetings which became a code word for arranging pro-democracy protests last spring.