We usually take it for granted that we can have complete and unrestricted access to the Internet wherever we are these days, but a recent study by an international group of researchers has illustrated exactly how wrong this notion is.

I am not talking about the lack of connectivity, or how hard it is to get a Wifi signal. What I mean is something more insidious: the state-sponsored filtering and blocking of objectionable Internet Web content and other applications by various countries around the world. As the authors involved in the OpenNet Initiative say in their new book, Access Denied: “Claiming control of the Internet has become an essential element in any government strategy to rein in dissent – the twenty-first century parallel to taking over television and radio stations.”

What surprised me the most wasn’t that filtering exists, but how many places do it. Certainly, government-sponsored filtering isn’t new – many public libraries and schools have done it for years here in the US, and hate speech is filtered in several European countries. But what is new is how much is filtered, and how sometimes it is disguised: some countries return a facsimile of an IE error page instead of showing that a site has been deliberately blocked.  Others tamper with their domain name servers to introduce errors when searching for particular sites.

The group collected data during 2006 the hard way – by actually sending in researchers and trying to view various Web pages and run specific applications by connecting to various Internet providers in each country. Some places were too risky, such as Cuba and North Korea. Other places were too big to get a handle on such as Russia. They found filtering in 26 out of 40 nations they visited.

The two biggest blockers (in terms of the number and type of sites) are Iran and China, no surprises there. Both countries block by keywords in the URL stream. China blocks ranges of specific IP addresses, too, and in fact has the most extensive filtering system that implements blocks at various network levels and across the widest range of topics.

Most of the book’s results are available online, and the group did a great job of defining the extent of Web filtering by various kinds of metrics, such as politics and power, social norms and morals, and national security concerns. Different countries filter for different reasons, too. For example, Syria filters a lot of political sites but fewer in other areas, while the Emirates and Saudi Arabia filter out a lot of what they consider objectionable social content. “Filtering directed at political opposition to the ruling government is a common type of blocking that spans many countries and is characteristic of authoritarian and repressive regimes,” say the authors.

There are some big gaps in the research: for example, at some point during 2006 you couldn’t connect via Skype in the Emirates, Jordan, and  Myanmar. Syria and Vietnam also blocked other VOIP providers. Other countries block free-email providers, and some such as Syria, Ethiopia, the Emirates, India and Pakistan also block free blogging providers such as blogspot. It would be nice to update this information with more recent conditions as well as to include other Internet communications tools in future surveys, such as WordPress and Typepad. You can add these suggestions online.

Another aspect of the filtering debate is that it is very ephemeral: not all filters are active all the time, and some countries only put up blocks during elections or other critical time periods when they want to exert more control over the free flow of information. This makes it difficult to present real-time results that have any accuracy, too.

And lest you think that filtering is more apropos to Asian and African nations, here in North America we have had some moments too. In July 2005, the Canadian provider Telus blocked access to the Web site run by the Telecommunications Workers Union during a labor dispute, to say nothing of our own government’s Internet surveillance activities,

So what are some lessons for those of us that travel internationally to these countries? First, use a VPN to connect back to your American provider to try to avoid the blocks. If your company doesn’t have one, there are dozens of free and low-cost VPN providers that can help. Second, be careful about the keywords and URLs that you use when you are browsing the Web from abroad. Finally, if you use a free blogging, Web, or email service, expect that you might not have access to these services when you travel.

As the authors say, “The Internet has borders – just like meatspace – and the quality of its borders depends on the situation of the country that erects them.”