'Jihobbyists' are people drawn to the online theater of violent jihad, becoming increasingly radical as they delve deeper into Web forums. Colleen LaRose, also known as 'Jihad Jane,' is an example of this threat, according to counterterrorism experts.

The same holds true whether it's a group of "jihobbyists" praising the latest attack by Muslim extremists or the tiny weirdo fringe that thinks Timothy McVeigh was justified in blowing up the Alfred P. Murrah Federal Building in Oklahoma City.

The third tier of the Jihadist movement comprises those individuals, cells or groups who emerge without direct assistance, training or support from any official al-Qaida element. Some call them "self-starters," others refer to them as practitioners of "home-grown terrorism." Crucially, they come to the movement of their own volition. They may be guided by teachers, friends, mentors or religious figures, but they largely drive their own radicalization. This book coins a new term for such enthusiasts of the global Jihadist ideology: Jihobbyists.