Micah Zenko, at the Council on Foreign Relations blog, points to  a recently declassified report from the Government Accountability Office (GAO) on the spread of drones. The report, Agencies Could Improve Information Sharing and End-Use Monitoring on Unmanned Aerial Vehicles , finds:
“Since 2005, the number of countries that acquired an unmanned aerial vehicle (UAV) system nearly doubled from about 40 to more than 75. In addition, countries of proliferation concern developed and fielded increasingly more sophisticated systems. Recent trends in new UAV capabilities, including armed and miniature UAVs, increased the number of military applications for this technology. A number of new civilian and commercial applications, such as law enforcement and environmental monitoring, are available for UAVs, but these applications are limited by regulatory restrictions on civilian airspace.
“The United States likely faces increasing risks as countries of concern and terrorist organizations seek to acquire UAV technology. Foreign countries’ and terrorists’ acquisition of UAVs could provide them with increased abilities to gather intelligence on and conduct attacks against U.S. interests. For instance, some foreign countries likely have already used UAVs to gather information on U.S. military activities overseas. Alternatively, the U.S. government has determined that selected transfers of UAV technology support its national security interests by providing allies with key capabilities and by helping retain a strong industrial base for UAV production. For instance, the United Kingdom and Italy have used UAVs purchased from the United States to collect data on Taliban activity in Afghanistan.”