Cyber Vigilantes Track Extremist Web Sites, Intelligence Experts Balk at Effort MIAMI, Fla. — While the debate grows on how to tackle global jihadism on the Internet, some security experts warn that "cyber vigilantes" — people who track and help shut down terror-related Web sites — are compromising government investigations with their amateur sleuthing tactics. Michael Radu, a senior fellow at the Foreign Policy Research Institute and an expert on terror-related Web sites, said the government is already overburdened trying to monitor the thousands of sites on the Web believed to contain radical Muslim messages. These cyber vigilantes, he said,...