Web censorship by governments for political, social or 'national security' reasons is increasing, according to a global survey by the OpenNet Initiative. 

John Palfrey, executive director of the Berkman Center for Internet and Society, and clinical professor of law at Harvard Law School, believes the survey shows that online censorship is growing around the world. 

"Some regulation is to be expected as the medium matures, but filtering and surveillance can seriously erode civil liberties and privacy, and stifle global communications," he said. 

The survey focused on geographical areas, such as Asia, the Middle East and North Africa, and found that 26 of the 41 countries surveyed block or filter internet content.

According to the study, censorship is expanding into new countries and becoming more sophisticated over time.

Countries are not only blocking websites that show pornographic pictures, information about human rights or YouTube videos, but applications such as Skype and Google Maps. 

The study found three primary rationales for filtering:

Politics and Power leading to the filtering of political opposition groups, common in many of the countries surveyed

Social Norms leading to filtering of subjects deemed offensive to social norms, such as pornography, gay and lesbian content and gambling, also common in many of the countries surveyed.

Security Concerns leading to the filtering of sites that could endanger national security, such as websites of separatist and radical groups including the Muslim Brotherhood in some countries in the Middle East. 

The report claimed that Iran, China and Saudi Arabia not only filter a wide range of topics, but block a large amount of content related to those topics.

South Korea's filtering efforts are very narrow in scope, but heavily censor one topic: North Korea.

Countries engaged in substantial politically motivated filtering include Burma, China, Iran, Syria, Tunisia, and Vietnam, according to the OpenNet Initiative.

Saudi Arabia, Iran, Tunisia and Yemen engage in substantial social content filtering, while Burma, China, Iran, Pakistan and South Korea have the most encompassing national security filtering, targeting websites related to border disputes, separatists and extremists.

No evidence of filtering was found in 14 countries, including Afghanistan, Egypt, Iraq, Israel, West Bank and Gaza, Malaysia, Nepal, Venezuela and Zimbabwe, many of which might be expected to filter internet content.