[MaximumYComb]

I wouldn't be surpised if there are over 50k individuals in the US with the electronics/computer knowledge to pull this off. All it takes is one person to develop an obsession with it and spend the time needed to pull it off. If you look at a 10-20 year time frame I'd say there's a high certaintity that someone commits a terror attack via a large number of drone.

The saving grace here is that people who want to terrorise often aren't the same with these skills IMO. If you have the skill/knowledge to make a drone swarm you probably have other valuable skills, have a good job and live comfortably. Lower chances of radicalisation.

[AnimalMuppet]

You're looking at it backwards. Some of those who are already radicalized have the background and mental capacity that they could learn the knowledge needed to pull this off. Al Qaeda didn't radicalize pilots; they sent radicals to flight school.