Social media sites are increasingly being used by radical organizations as platforms to broadcast their ideology and recruit followers and finance. The goal was to provide a computational model for early detection of such individuals. Two research questions are studied. First, how does extremism portray in users’ activities on YouTube and how does this activity vary over time? Second, can we predict whether users are at risk of radicalization; that is, will users with a history of activity in communities with milder versions of radical ideologies, transition to participate in more extreme communities?