Great firewall of China

With an estimated 137m people online and a Communist party that sees “thought guidance” as a cornerstone of its power, China has become the greatest test of the ability of authoritarian regimes to tame the internet.

Beijing leaders, who have long practised censorship of the media, consider the internet essential to a modern economy and as a potentially potent source of political threat.

To minimise the risk, Beijing has developed a multi-layered system of controls that starts with the “Great Firewall”, which blocks access to tens of thousands of websites judged inappropriate.

Within China, the systems involve public and state security departments that monitor online activity and occasionally detain or arrest journalists or online authors overtly critical of the political system or who reveal inner details of its workings.

Party and state censors also punish internet companies that allow the distribution of suspect content, a policy that means companies shoulder most of the burden of keeping it off the web.

The goal is total control of content but to keep most websites to which ordinary Chinese can access within vaguely defined boundaries – and to maintain the ability to quickly identify and isolate individuals who appear to be threats.

Despite its scale and sophistication, the system is secret. Beijing officials generally admit to trying to block pornographic sites and to trying to suppress “rumour-mongering".

The result is that while sophisticated users can usually gain access to any overseas online content, most people have little way of know the degree to which their internet experience has been filtered by fiat. A drive to “purify” the internet announced by President Hu Jintao suggests an aim to further reduce online liberties.