Saudi men talk and browse the internet at a hotel in Riyadh. Photograph: Kamran Jebreili/AP

Saudi Arabia leads the field among Arab regimes that practise internet censorship, blocking website content ranging from pornography to politics, but also in waging a highly effective online war against al-Qaida and other jihadi groups.

According to the OpenNet Initiative (ONI), the conservative kingdom operates a “sophisticated” filtering system run by the internet services unit at King Abdulaziz City for Science and Technology in the capital Riyadh.

Blocking is done according to two lists: one of “immoral” (mostly pornographic) sites; the other based on directions from a security committee run by the ministry of interior. Citizens are encouraged to actively report “immoral” sites for blocking, with hundreds of requests made every week.

“The internet is one of the most heavily censored areas in Saudi Arabia,” said Madawi Al-Rasheed, of King’s College London, whose own Arabic website is blocked in her homeland. “But it is quite easy to circumvent using proxy servers. The idea is to protect society, but the so-called immoral sites are the most accessed, much more than radical or jihadi ones.”

After Egypt, Saudi Arabia has the highest number of bloggers in the Middle East, many of them women who use pseudonyms to avoid trouble with the authorities.

In Syria, which has a secular authoritarian regime, at least 160 websites related to opposition parties, Kurdish groups and hostile media organisations are banned. A “clean hands” site, set up to campaign against corruption, was shut down after a banning order was issued.

Controls are being tightened as the government tries to keep pace with increasing computer use. Censors are also becoming more advanced technologically, their work made easier by the fact that all internet traffic must pass through two state-controlled servers.

Cafes and other public internet centres need operating approval from the security services and are required to keep detailed records of customers’ surfing habits. Like most Arab countries, Syria blocks all Israeli websites.

Internet censorship in the United Arab Emirates, another Middle Eastern blackspot, is “substantial”, according to the ONI. Reporters Sans Frontieres (RSF) categorises it as “an enemy of the internet”. In 2006 the government passed a law against “information crimes”. It criminalises “those providing the web with content that harms public order or moral values”. The maximum punishment is five years in prison.

The telecoms regulator blocks websites deemed offensive to local culture or values. Pornography and gambling sites are blocked by local telecoms providers.

Tunisia is in ONI’s “pervasive” category and on RSF’s “internet enemy” list. The secular, western-backed North African republic blocks thousands of websites. “The Tunisian government has realised that censorship is not working the way it wanted it to,” says blogger Sami ben Gharbia. “The flow of dissident information into Tunisia is a fact and censorship is simply not succeeding in stopping it. The government is updating its policy from a simple blocking of dissidents’ websites and blogs to a much more aggressive one, that includes hacking and deleting websites and filtering emails.”

Ian Black