Terrorism's Hook Into Your Inbox

In a recent analysis, Weisburd examined a number of Internet sites residing on a Web server also used to host a jihadist site. Weisburd said he found numerous counterfeit online banking sites, the sort typically set up by scam artists to steal personal and financial data from consumers.

"In short, the terrorist Web site was the most legitimate site on the server," Weisburd said. "In an age when people sign themselves up for the cause and make a good faith effort to try and kill people, credit card fraud and identity theft is a crime [terrorist sympathizers] can get into from the privacy of their own home. Pretty much wherever there are jihadists active online, you will also find guys engaged in online fraud."

Weisburd said credit card fraud and the cyber crime methods that facilitate it are ideally suited for upstart terror cells seeking funding. The Carbondale, Ill.-based activist said he also sees a great deal of overlap in membership between the Arabic-language online hacking forums and those of the online jihadist community.

"If they don't know how to get started in online fraud, these guys can find all kinds of support from people who will gladly teach them how to do it."

If Tsouli helped to pioneer a number of methods for the jihadist forums, jihadist groups have since moved their Internet operations further underground. Experts said most of the major forums have since consolidated their operations into small number of password-protected forums known as the Al Fajr Center.

"By keeping the number of primary source jihadist Web sites small, online ideologues and leaders of various jihadist groups can provide a seamless way to authenticate their communications, allowing forum participants to instantly tell the difference between official and fake communiques posted to the forums," Katz said.

Still, Katz said, Irhabi's legacy lives on. His hacking and anonymity tutorials are widely traded on jihadist forums, and variations on "Irhabi" -- such as Irhabi008 and Irhabi009 -- remain some of the most popular screen names on those sites.

Groups that monitor jihadist Web sites and chat rooms say most operate almost entirely using infrastructure and commercial services based in the United States. While some anti-terror groups advocate an aggressive dismantling of U.S. based jihadist networks, others say U.S. intelligence services need to do more to infiltrate and learn from them.

"We need to better understand who the primary actors are on these sites and chat rooms, as well as the nexus between where these people are in the cyber and physical world," said Frank J. Cillufo, director of the Homeland Security Policy Institute at The George Washington University. "Sure, people will say and do things in the cyber environment that they probably wouldn't do face-to-face, but the question is when does it morph from talk into action? We need to better understand the trigger points that move these participants from sympathizer to activist to indiscriminate violence."

In testimony submitted in February at a hearing in the House Armed Services Committee, the SITE Institute presented several recent case studies where jihadist forum participants or administrators transitioned from online activists to combatants fighting U.S. coalition force in Iraq and Afghanistan.

"U.S. authorities must continue to study the Internet as a vital battleground in the war on terror and undertake further efforts to combat jihadists on this front," Katz said. "Delving efficiently into the online world of jihadists will be one significant step in the war on terror."