More about the French drones cited by FlamantRose above from the BBC
here:
Air force spokesman Col Jean-Pascal Breton said all the drones involved were small-sized and commercially available and because of their size they were not considered a threat.
On French TV news yesterday evening, a French air-force spokesman also mentionned that "the drones were not detectable by military radar", only by visual observation...?!
The possibilities of who is behind these French drones are almost endless: Al-Qaeda or some other terrorist organisation; hackers trying to discover and eavesdrop on wireless networks operating at the power stations; Google map street view etc.
My own opinion is that it is Amazon.com, experimenting with their drone delivery service in a "controlled-airspace" where all other flying objects should normally NOT be found...?!