CAIRO, Egypt — In Iran, a large red icon pops up on computer screens. In Syria, there's a discreet note from the filter. Other Arab nations display "blocked" in bold lettering or issue crafty "page not found" replies.
However the censors put it, the message is clear: You're not permitted to see this Web site.
Governments in the Middle East are stepping up a campaign of censorship and surveillance in an effort to prevent an estimated 33.5 million Internet users from viewing a variety of Web sites whose topics range from human rights to pornography. As a result, millions of Middle Easterners are finding it harder by the day to access popular news and entertainment sites such as Facebook, MySpace, YouTube and Flickr.
Five of the world's top-13 Internet censors are in the Middle East, according to the most recent report from Reporters Without Borders, the journalism advocacy group that lobbies against Web censorship.
"The Web makes networking much easier, for political activists as well as teenagers," Reporters Without Borders said in its annual report for 2007. "Unfortunately, this progress and use of new tools by activists is now being matched by the efforts of dictatorships to fight them. Dictators, too, have entered the world of Web 2.0."
Internet regulations vary widely across the Middle East. Predictably, the most authoritarian governments have the most aggressive filters, but even some without advanced censorship systems have prosecuted bloggers for controversial postings on religion or politics.
Just as Internet users have banded together on social networking sites to challenge the wave of censorship, the region's governments also are uniting to share filtering software and the latest online surveillance technology, activists said.
"Now there's some common work among the Arab governments to censor the Internet. They're acting like they're fighting terrorists," said Ihab al Zalaky, the managing editor of a respected Egyptian newspaper and the chief author of a comprehensive report last year on regional Internet censorship. "There's no good news. They're all making it harder for people to access the Internet."
Only four Arab countries have little or no filtering: Lebanon, Morocco, Jordan and Egypt — but Egyptian politicians are considering a law that would criminalize some online activity.
At the other end of the spectrum are Saudi Arabia and Syria, consistently described by human rights groups as the most hostile toward the Internet. The rest of the region falls somewhere in between, with governments importing the latest technology to narrow the number of sites available to the public and drafting laws to curb online dissent.
The prohibitions have led to an explosion in circumventors, proxy servers that allow Internet users to bypass workplace or government filters. In cyber cafes from Damascus to Dubai, patrons furtively browse blocked sites and swap Web addresses for the latest "proxies."
The most tech-savvy young Arabs and Iranians use new proxies every day, trying to stay a step ahead of government censors.
"We've seen on the one hand an increase in Internet usage throughout the region and, in reaction to that, we've seen governments getting more sophisticated in how they arrest people and censor online content," said Nadim Houry, a Human Rights Watch researcher for Lebanon and Syria. "It's sort of the traditional cat-and-mouse game."
Last month, Syrian authorities banned several more sites, including the book and music vendor Amazon.com. The government reportedly uses a filtering system called Thundercache to block content from sites such as Blogspot, Hotmail, Skype and YouTube. Many Arabic-language news sites also are banned.
In Iraq and the Palestinian territories, the Internet is policed mainly by the owners of Internet cafes and by Internet users themselves, according to monitoring groups. In both places, Islamist militants have attacked Internet cafes, accusing patrons of looking at pornography or chatting with members of the opposite sex.
In Iraq, the U.S. military is the only official Internet censor — operational security measures prevent American troops from using some sites and commanders have shut down cyber cafes in areas where insurgents use the Internet to share intelligence and plot attacks.
More typical is the censorship that's spreading throughout Arab states in North Africa. Tunisian authorities block several sites, human rights workers said, but they've also begun to hold the owners of Internet cafes liable if political activists use their establishments to post critical news about the government.
After years of Internet freedom, Sudan reportedly has purchased a state-of-the-art blocking program that prohibits access to political sites and literary works that range from racy fiction to a book that the government deemed offensive to Islam's Prophet Muhammad. Morocco, Algeria and Libya also have come under fire from human rights watchdogs because of their prosecution of online dissidents.
In Egypt, the Arab world's most populous nation and home to an estimated 6 million Internet users, the government offers cheap dial-up browsing to anyone with a telephone line and authorities do little or no filtering, so video-sharing platforms, social-networking sites, most opposition sites and pornography are all easily accessible.
But police have rounded up at least three bloggers and harassed many more in recent years, according to Reporters Without Border. Activists also fear more filtering after an Egyptian court last year ruled that authorities could block, suspend or shut down any Web site that could pose a threat to "national security," vague wording that could lead to criminal charges for dozens of Egyptian bloggers.
Abdel Moneim Mahmoud, 28, has been arrested and harassed by Egyptian authorities several times in connection with his blog promoting the Muslim Brotherhood, a powerful Sunni Islamist opposition group. Because he uses Blogspot, the U.S.-based weblog platform, the Egyptian government hasn't been able to block his blog without banning the site altogether.
"They threatened, 'If you don't stop blogging, we will arrest you' every month," Mahmoud said. "Police officers ask about specific things on our blogs when they call us in for investigation. They use IP-address tracking to find out who is writing which blog."
Iran's hard-line Shiite Muslim leadership is another zealous censor of the Internet. The government boasts of filtering 10 million "immoral" Web sites in addition to all the major social networking outfits and dozens of pages about religion or politics.
For the past year, according to human rights groups, Iranian authorities also have zeroed in on online publications dealing with women's rights. Two prominent "cyber feminists" were arrested in the past month on charges of distorting public opinion and drawing negative publicity to Iran through the postings on the Web.
Across the Persian Gulf from Iran, the Arabian Peninsula is home to some of the world's most stringent censors, with Saudi Arabia at the top of the list. Qatar, Kuwait, Bahrain and Oman are among other Gulf countries that filter online content.
Even in a place as glitzy and modern as Dubai, the regional shopping hub in the United Arab Emirates, a strict filtering system targets pornographic and political sites. Dubai residents can drink and party all night long, but they're not allowed to read about such exploits on some blogs penned by Western expatriates.
Earlier this year, residents were outraged by tentative plans to extend the censorship to so-called free zones, where media and multinational companies can — for now — surf the Web unfiltered. Foreign workers in Dubai have decried the ban on voice software such as Skype, which allows them to call home for free. Critics call it economic censorship of the Internet, an attempt by state-backed telecommunications firms to build their revenue from international calls.
The ultraconservative Saudi government, a close U.S. ally, blocks thousands of Web sites that deal with pornography, religion, politics and human rights. Medical students at Saudi universities have complained that they can't even access scientific sites to study human anatomy.
Fed up with the growing list of banned sites, a 25-year-old finance student named Hani Noor helped his cousin to create a Facebook group called, "We All Hope They Don't Block Facebook in Saudi Arabia." As of Monday, the group had 225 members and a message board that focused on tips for the best proxies to get around government bans.
Noor, however, hit on an even better solution: he signed up for satellite Internet, which means his connection is now free from the long arm of the Saudi censors.
"I'm off the hook," Noor said with a triumphant laugh in a telephone interview from his home in Saudi Arabia. "We are winning. They're blocking, but we've always found a way to overcome it."