An increasing number of governments around the world want to filter what people read on the internet, according to an academic study.
State-based internet filtering is on the rise - not only in the sheer number of governments engaging in content filtering but also in the scope of the material they're blocking, according to the report, which was presented Friday at a conference in Oxford.
The year-long study is the work of the OpenNet Initiative (ONI), launched by four universities: Cambridge, Harvard, Oxford and Toronto.
"There is a very clear trajectory from less filtering to more filtering, and it's happening in a more sophisticated fashion," said co-author John Palfrey, executive director of the Berkman Center for Internet and Society at Harvard Law School.
Palfrey pointed to a rise in the number of specific web sites and services being blocked by governments, such as Skype, the user-generated video site YouTube and the searchable maps and satellite imagery application Google Earth.
Governments are increasingly targeting "applications that allow people to do things a state might think is subversive", he said.
China, Iran and Saudi Arabia are among the top blockers. More than half of the 41 countries surveyed by ONI were found to block or filter online content.
The filtering covers a wide range of pornographic, political, human-rights and religious websites.
Filtering is also on the rise in industrialised areas, such as Europe, according to Palfrey. "There is, for instance, growing pressure to filter child pornography in Great Britain," he said.
Whether internet filtering is good or bad is an "open question”, Palfrey said. "Some people would say that certain kinds of information should be banned." Even the First Amendment to the US Constitution, which protects freedom of speech, "has restrictions", he added.