Repressive governments no longer limit themselves simply to blocking access to websites they want to keep from their citizens.

Increasingly, experts on internet censorship say, they are turning to a range of other techniques, from methods developed for “cyber-warfare” to the filtering-out of specific content deemed undesirable. In the process they have been relying on private companies, many from the US and other liberal regimes, to supply the technical know-how and, in some cases, act as their eyes and ears in cyberspace.