Drones: Next generation terror weapon against civilian targets?

“The cheap commercial drone the militant group deployed to bomb Syrian rebels in Aleppo could soon be seen above battlefields all over the world—and it’s way ahead of U.S. defenses.”
Large military drones are familiar to most of us, recognized as highly effective reconnaissance and attack craft. But hobbyist drones as weapons of war? In an article appearing in today’s The Beast, Hezbollah Drone Is a Warning to the U.S., the focus was on just these as a military delivery vehicle on the battlefield. The Beast limited focus to Hezbollah’s use of small drones dropping mini-bombs on Allepo, Syria. But we live in the post 9/11 age of the War on Terror in which the entire world is today threatened, must also be considered a military “front.” And the popularity of drones has exploded in recent years. Civilian models range in quality and sophistication from in-house toys to outdoor machines fitted with gps, gyroscopes and high definition video cameras. A quick look at Amazon’s opening page provides a range in price from $41.90 to $1192.30.
A January 26, 2016 article that appeared in The Guardian described American consumers having purchased Nearly 300,000 civilian drones registered in US in 30 days. Three-hundred thousand drones as likely holiday gifts in a single month! The article quotes the FAA reporting that Unmanned Aerial Vehicles (UAV’s) are being registered at a rate of 10,000 per day. And since the law regarding civilian drone registration only came into effect in mid-December, 2015, there may be upwards of a million such “toys” in use in the United States alone. And with the lax legal restrictions on gun sales in that country, weaponizable UAV’s should find little difficulty finding their way into a “lone wolf” terrorist’s hands.
And so the question: How determine whether a drone hovering over, say, a football stadium in Newark is operated by a “hobbyist” peeking at the game, or a “terrorist” on a mission?