mass casualties. The perpetrators of 9/11, however, clearly wished to kill as many people as possible. The actions of the Al Qaeda leadership and their statements both suggest that if they could acquire these weapons, they would deploy them. The difficulties of acquiring, transporting, and successfully deploying these types of weapons are such that this is a very-low-probability event. But the consequences of a successful deployment of even the easiest of them, a radiological device, would be so catastrophic that there is no responsible option but to defend against them.
We cannot accurately predict how terrorists will next choose to attack us. Historically terrorists have been very conservative in their use of tactics, preferring simple tried technologies, given the conditions of uncertainty in which they operate. Hence, bombs and bullets have been tools of choice. However, the psychological payback of a successful deployment of even a crude chemical or radiological device is such that some terrorists are likely to try to acquire these weapons.
Still, the probability is higher that terrorists will attempt an attack with conventional explosives that can be acquired very easily but when strategically deployed can inflict significant casualties and even great psychological damage. The diffuse nature of the threat, and the fact that many militants operate largely independently of any central command, suggest the need to be prepared for all types of attack as well as the fact that different types of attack could be planned simultaneously.
Particular branches of fundamentalist Islam have proven to be very successful in attracting a range of different individuals to the jihadi cause and in so doing making it impossible to single out those to track. These range from poor uneducated young men from the Middle East and North Africa, to middle class, computer-literate, and Western-educated young men from the region, as well as first- and second-generation Muslims living in the West. They have also won converts to the cause via the Web, prisons, and personal networks. There is no simple profile of the terrorist; rather, the background of those participating in violence is constantly expanding and increasingly including formerly excluded categories of individuals. The anonymity of the web, for example, permits the participation of women.
The most important of these new technologies is information technology, and in particular the Internet—Al Qaeda could not function without it. Today, Islamic fundamentalist terrorist groups rely on the Internet to communicate with their members, their supporters, and one another across the globe. They use the Internet to recruit members by hosting Web sites detailing the iniquities of their adversaries, the successes of