The vehicles can be adapted to offensive purposes using toys, off-the-shelf components and a basic or rudimentary knowledge of the science behind a simple device that can be programmed for a destination or manipulated from a remote control.
UAVs that depend on an outside control, increasingly dubbed Unmanned Airborne Systems, are no longer the preserve of multimillion-dollar military establishments.
Several recent surveys identified countries hostile to the West among those possessing UAVs of different capabilities. Neither the numbers nor the names of countries that own UAVs or UAS are reliable or complete, analysts said.
U.S. MQ-1 Predator UAVs armed with Hellfire missiles are increasingly used in combat operations against suspected terrorist targets in Afghanistan, Pakistan, Somalia and Yemen.
"iUAVs come in all shapes and sizes, and though not a threat at the level of a fuel-laden airliner, they can be used as an effective surveillance platform and weapon of terror against a variety of targets," Florida website uavthreat.com said.
London's Guardian newspaper surveyed the global UAV scene, concluding with data columns where key information was still missing because it wasn't known. UAV makers now include Iran and other countries whose policies are at odds with U.S. and allied nations in the West, Asia and Europe.
In Latin America, UAV development has been driven by the need to secure borders against organized crime, narcotics and people smugglers and poachers.
Brazil is in the forefront of technology transfers from Israel and Europe aimed at developing its own UAV manufacturing capability.
A $358 million U.S. Army project aims to upgrade 45 RQ-7B Shadow UAVs to work in tandem with AH-64 Apache helicopters to enable a combat capability involving little direct human interaction.
An Apache crew flying in relative safety should be able to engage a hostile target by firing a small missile from a UAV cruising some distance away, without having to put the crew in danger, Defense News reported on its website.
AAI Unmanned Aircraft Systems, manufacturer of RQ-7B Shadow, said the upgrade would aim to weaponize the UAV by increasing its wing span. AAI, a unit of Textron Systems, has headquarters in Hunt Valley, Md.
Weaponization of UAVs has followed recent combat experience.
U.S. forces in Afghanistan complained they lost track of at least 90 insurgents who were observed emplacing improvised explosive devices because the UAS that was tracking them didn't have a lethal component.
Armed Shadows "might have engaged the enemies who were exploiting existing sensor-to-shooter time," the U.S. Navy wrote in a funding request.
As modifications in UAVs increase, the specter of hostile elements doing the same while seeking to deploy UAVs and UAS -- UAVs backed by ground controls -- geared toward terrorist acts.
UAVs weighing as little as 5 pounds could be airborne very soon, with larger models allowed in the next two years, Air Facts Journal, which reflects pilots' concerns, said on its website.
The growth in the number of UAVs sharing the same air space as passenger airlines has raised major security questions.
"America's wars of the last decade have vaulted the UAV from novelty to workhorse. Yet too little is being done to prepare for the inevitable day when our enemies turn these weapons, which are growing cheaper, more powerful and more ubiquitous, against us," Darin L. Gaub said in an article on armedforcesjournal.com website.