ISIS already use drones in battlefields for information purposes, but now next step use them for an attack. And they will be more effective than attacking with guns. In Paris, they tried to get into Stade De France. Luckily people at the gate stopped the terrorist, and they exploded the bomb outside the stadium. But think that, they were using drones, they can not be stopped even at night you can even hardly saw them. Bomb equipped drones can crash land on the people or soccer players. That may cause many causalities.
The U.S. Government realize the treat, in the battlefield, they are targeting drones of ISIS. Also, there is a new law that every drone owner should register their flying machines to FAA. And the near future I would like the see a small drone killer lasers that produce by Boeing for burning the drones while they are on the air. They can make this laser for police vehicles shot them down.