A report released today by the OpenNet Initiative (ONI) concludes that the scale, the scope, and the sophistication of state-based Internet filtering have all increased dramatically in recent years. The survey highlights the tools and techniques used by countries to keep their citizens from viewing certain kinds of online material.

ONI is a collaboration among four leading universities: Cambridge, Oxford, Harvard, and Toronto. The group's testing was carried out during 2006 and early 2007. ONI used a combination of tools that can remotely test filtering conditions within given countries. The group also relied heavily on local researchers who evaluated Internet conditions from inside certain countries. Some countries, such as Cuba and North Korea, were deemed too dangerous for either remote or in-country testing. But of the 41 different countries tested by ONI, 25 were found to block or filter online content.

"Over the course of five years, we've gone from just a few places doing state-based technical filtering, like China, Iran, and Saudi Arabia, to more than two dozen," says John Palfrey, executive director of the Berkman Center for Internet and Society at Harvard Law School. "As Internet censorship and surveillance grow, there's reason to worry about the implications of these trends for human rights, political activism, and economic development around the world."

But it's not just the sheer number of countries doing content filtering that has grown; it's also the breadth and depth of material being blocked.

The report discusses three primary rationales that nations have for blocking Internet content. The first is political, which leads to, for example, the blocking of opposition-group websites. The second rationale is social: some countries block pornography and sites dealing with gambling or sexuality issues. The third rationale is national security, which can lead some nations to block online material produced by, for example, extremist groups.

According to the report, China, Iran, and Saudi Arabia remain the top blockers. Each nation filters not just pornography, but also a wide range of political, human-rights, religious, and cultural sites deemed subversive by those countries' governments.

Other countries are more selective in what they let citizens see or not see. Syria and Tunisia, for example, filter a great deal of political content, while Burma and Pakistan target websites that pertain to national-security issues.

One interesting case is that of heavily wired South Korea, where ONI found Internet filtering limited to one topic: North Korea. "The South Koreans block several North Korean websites," says Nart Villeneuve, director of technical research at the Citizen Lab at the University of Toronto. "They even tamper with the system so that when you try to access one of those North Korean sites, the URL resolves to a South Korean police page telling you, 'What you're trying to access is illegal, and we know your IP [Internet protocol] address.'" (An IP address could be used to locate the computer where the search is conducted, with the ultimate goal of identifying the individual involved.)