Unfortunately, a rather low-tech drone using commercially available GPS homing and the like would be an excellent terror tool and extremely difficult to interdict. Payload would be quite limited in weight and volume, however.
The “Payload” is the whole point behind Drones and although not an entirely technologically prohibitive tool for those who have not developed and fielded such a weapon to date, it is not such a simple technology to master when you consider using it as an offensive weapon other than a “kamikaze” drone.
Too many people overestimate the actual feasibility of this tool at this time. To suggest that ISIS will soon be sending waves of Drones into the U.S. manned with Hellfire type missiles to terrorize Americans is absurd.
That will change in the future as technology advances along with the availability of such platforms, but currently it is simply a propaganda tool, IMO.
“Payload would be quite limited in weight and volume, however.”
Yes, but a drone that can lift a heavy camera can also lift enough C4 to ruin your day. A swarm of those would be handy tools for targeted assassinations.