Explosive drones: How to deal with this new threat?

As the commercial and recreative use of small unmanned aerial vehicles or drones is booming, so are the military and criminals starting to use these systems more and more. Due to improvements in flight stability, autonomy and payload capacity it becomes possible to equip these drones with explosive charges, making them threat agents where traditional response mechanisms have few answers against.  
In this paper, we will discuss this new type of threat in detail, making the difference between the loitering munition, as used by regular armies and the traditional drones equipped with explosive charges, used in guerrilla warfare and by criminals. We will then discuss what research actions are currently being undertaken to provide answers to each of these threats and what countermeasures that are currently already available and which ones will be available in the near future.