Yahoo! Tech is reporting that an expert on terrorist activity on the Internet, Evan Kohlmann, warned that terrorists are recruiting using Internet websites and forums. The remarks were made at the International Conference on Cyber Security in New York. 

Kohlmann warned that taking down such sites from the Internet is insufficient, saying that “you knock one out, another one pops up the next day.”

“Infiltrating the system is most effective," he said. "People don't know if you're a real jihadi or an agent. These people have never met each other and if you give them a reason not to trust each other, that's all it takes,” Kohlmann was quoted as saying in the report.

Other experts have also warned that terrorist sympathizers were posting instructions on how to build weapons and other items necessary to commit violence on radical Islamic message boards. Adnkronos International reported on July 9, 2008 that web site had published a manual on how to build car bombs that could be detonated by remote control.

The warnings are substantiated by a recent report in The Scotsman that radical Islamic groups in the United Kingdom were using Facebook, a popular social networking website, to recruit. The report said that one of the successors to the Al-Muhajiroun group, which has been banned as a terrorist organization, ran a group on Facebook that provided links to sermons by radical Islamic preachers that justified terrorism.