The FBI has investigated more than 100 suspected Islamic extremists within the U.S. military, about a dozen of whom are considered serious threats. According to NPR:
The FBI and Department of Defense call these cases "insider threats." They include not just active and reserve military personnel but also individuals who have access to military facilities such as contractors and close family members with dependent ID cards.
Officials would not provide details about the cases and the FBI would not confirm the numbers, but they did say that cases seen as serious could include, among others things, suspects who seem to be planning an attack or were in touch with "dangerous individuals" who were goading them to attack.
