Shortly after 9/11, Glen Jenvey, an unemployed truck driver living near Stonehenge, began pretending to be a Pakistani man who believed in violent jihad. His counterterrorism, which took place in the second-floor study of his stone house, helped lead to the arrest of Abu Hamza al-Masri, one of Europe's most vitriolic clerics.

"You have to hand it to these people," says an Indian military official who spoke on the condition that he only be identified as "the brigadier." Jenvey and other cybersleuths have "done some real work that has had some real results."

Working as a private investigator in Sarasota, Fla., Bill Warner spends part of his day chasing errant spouses and the rest of his time tracking down jihadis.

Playing a game of Internet Whack-a-Mole, Warner has helped take down nine jihadi Web sites in the past six months, including one of the most important, Alhesbah, a principal forum for supporters of al-Qaida.

"I started with the Islamic Thinkers Society site in June of 2005, before it became all private and password protected," recalls Warner. "I downloaded a lot of their information and photos posted of U.S. servicemen being killed or their bodies mutilated after a firefight in Iraq or Afghanistan. I know what is posted on these Web sites; they need to be shut down."

Beyond patriotism, cybersleuths state four main reasons for getting involved in the fight:

-- Disruption of jihadi Web activities
-- Intelligence gathering
-- Amateurs are not bound by the legal restrictions governments are
-- Western governments aren't doing enough

Yet government, military and counterintelligence officials counter that cybersleuths may be doing more harm than good.