Internet censorship in Iran is amongst the most restrictive and sophisticated in the world, a technical study has revealed. And much of the filtering technology in use was developed by western companies.

The Iranian government employs extensive internet filtering to block out content deemed inappropriate, according to a new report issued by the OpenNet Initiative - a partnership between the University of Toronto in Canada, Harvard Law School in the US and the University of Cambridge, UK.

Researchers remotely accessed computers within Iran's internet borders to test the restrictions imposed by the government. The team used a variety of methods to test the filters - dialling into Iranian ISPs from outside the country, connecting to desktop machines using remote-control software, and routing traffic through dedicated servers within the country.

They found that 34% of the 1465 URLs they tested were blocked, including 100% of the pornographic websites tested. Many gay and lesbian web pages were blocked, as were those hosting politically sensitive content - 15% of blogs and 30% of news sites were inaccessible. Sites providing tools and information for circumventing filtering technology were also blocked in 95% of cases.

Technological change

A similar situation exists in China, where government-run ISPs routinely filter content they deem politically unacceptable. There is even evidence that the web commentators are employed by the authorities to post pro-government statements to weblogs and online message boards.

"Along with China, Iran has committed to adapting its filtering practices to changes in internet technology," says John Palfrey, a member of the OpenNet Initiative at the Berkman Center for Internet and Society at Harvard Law School. "Bloggers who write in Farsi in Iran have a much harder job today in trying to reach their audience than bloggers in most other parts of the world."

The OpenNet team found that the Iranian government relies on filtering technology developed by western companies to control internet use. "There is a growing market for censorship technology worldwide and the demand is being filled by western corporations," says Nart Villeneuve, a researcher at the University of Toronto in Canada.

"Increasingly, countries are deploying commercial filtering applications to filter pornography,” he says, “but also adding content that is blocked for political reasons."

Illegal and unauthorised

The researchers say Iran mainly employs a package called SmartFilter, developed by US company Secure Computing. However, Secure Computing told New Scientist that Iran’s state-controlled ISPs are using the company’s software without permission. "Secure Computing has sold no licenses to any entity in Iran," says spokesman David Burt. "We have been made aware of ISPs in Iran making illegal and unauthorised attempts to use of our software.”

Web surfers can defy government censorship by accessing sites through proxy web servers located outside their country, although access to these machines can also be blocked.

The US government established a proxy server for Iranian citizens in 2003, but this was later found to filter large sections of the internet itself. Programs that route data through ordinary desktop machines and disguise traffic provide a more sophisticated option.

The situation seems likely to get worse in the near future in Iran, following the election of an ultra-conservative president on Saturday 25 June. Mahmoud Ahmadinejad established himself as a religious hardliner during his time as mayor of Tehran and has alarmed western observers by vowing to continue with the country’s controversial nuclear program.