From the executive summary: "In mid-August 2016, the Shiite militant group Hezbollah reportedly dropped two small bombs from what is believed to have been a modified, commercially available drone that it was flying over rebel positions in Syria. While terrorist groups have long had a fascination with drones and experimented with their use, the incident was a first for a terror group, and it potentially represents the leading edge of a wave of similar incidents that could follow in the months, years and decades ahead. Much has been made of the threat of terror use of drones (also known as 'uninhabited aircraft systems,' or UASs), but little empirical and historical work has been done to support our understanding of this phenomenon and its evolution. This report seeks to address this gap by providing a review of, and framework to situate, cases in which terrorist entities have either shown a substantive interest in drones or have used them. It evaluates both individual use cases and the activity of groups that have used drones frequently enough to constitute their having a 'program.' These cases are then complemented by a review of the creative ways that private citizens have used drones, in order to provide decision makers with a firmer baseline of both demonstrated terror capability and what lies within the immediate realm of possibility, given what has already been achieved by others. This report also includes an overview of new technologies that are likely to further complicate the scope of this developing threat."
Combating Terrorism Center at West Point: https://www.ctc.usma.edu/