This is why drones are so tightly regulated in the US. The rules and regulations that apply for the research and recreational uses are not applicable for the military purpose drones that can fly according to the need of the national security.
However, the rules do apply to the UAVs used for research and recreational purposes, or for companies exempted by Section 333. These rules state that such drones cannot fly 400 feet or 120 meters above the ground. Also, they cannot be flown over large crowds or the property of other people.