It’s actually a potentially serious problem:

The technology for remote-controlled light aircraft is now highly advanced, widely available — and, experts say, virtually unstoppable.

Models with a wingspan of five metres (16 feet), capable of carrying up to 50 kilograms (110 pounds), remain undetectable by radar.

And thanks to satellite positioning systems, they can now be programmed to hit targets some distance away with just a few metres (yards) short of pinpoint accuracy.

Security services the world over have been considering the problem for several years, but no one has yet come up with a solution.

Sounds like a job for the hive mind of the blogosphere.