Maritime terrorism is not a serious threat. Acts of terrorism at or from the sea, that is to say acts of violence committed by politically motivated groups to inspire their supporters or induce feelings of fear among their enemies, have been rare and are likely to remain so. Insurgent groups do, however, use the sea. The maritime domain might offer few opportunities for terrorist acts but some insurgent groups have used it extensively.
The reason for the low incidence of maritime terrorism is that the risk-reward ratio rarely computes. The resources groups need to undertake acts of violence at sea tend to be specialized and therefore cost more than the resources needed to mount equivalent attacks on land. More important, the rewards terrorists look for, publicity in particular, are hard to achieve at sea because of distance, which limits press access, and because the effect on the audience is limited by the fact that few people think that what happens at sea affects them directly.