A small surveillance drone flew over the Austin stadium, diligently following a series of GPS waypoints programmed into its flight computer. On the face of it, the mission was routine.

Suddenly, the drone veered sharply off course, deviating from its intended flight path and hurtling east. After a few minutes, when it was clear that something was seriously wrong, the drone made a sharp right turn and headed south. Then, as if some ghost had ordered the drone to self-destruct, it hurtled toward the ground. Just a few feet from some kind of disaster, a safety pilot with a radio control device saved the drone from crashing into the scene.

On the sidelines, there were smiles all around about the near-disaster. Professor Todd Humphreys and his team at the University of Texas at Austin's Radionavigation Laboratory have just completed a successful experiment: closing a hole in the government's plan to open U.S. airspace to thousands of drones.

They can be turned into weapons

Spoofing the GPS receiver on a drone is just another way to hijack a plane

In other words, with the right equipment, anyone can take control of a GPS-guided drone and make it do whatever they want.

Spoofing is a relatively new problem in GPS navigation. So far, the main problem has been GPS jammer device, which are easily available via the Internet and used by people to hide illegal use of GPS-tracked company vans, for example. Iran is also believed to have shot down a US spy drone in December by jamming drone its GPS, forcing it into automatic landing mode after losing direction.

"Tricking the GPS receiver on a drone is just another way to hijack a plane." Todd Humphreys, a researcher at the University of Texas Radio Navigation Laboratory

Cell phone jammer can cause problems by disrupting GPS signals, while spoofers are a huge leap forward in technology. They can actually manipulate navigation computers with false information that looks real. He used his device - what Humphreys says is the most advanced spoofer ever built (which costs just $1,000) - to infiltrate the drone's GPS system and send out a signal more powerful than those coming from satellites high in Earth's orbit. .

Initially, his signal matched that of the GPS, so the drone thought there was nothing wrong. That's when he strikes - sending his commands to an onboard computer to get the drone to follow his lead.

Mr Humphreys said the impact was severe. "Within one to three years, the airspace will have 20,000 drones," he told Fox News. "Every one of them could be a potential missile aimed at us."

Drones have been widely used in places like Iraq, Afghanistan and Yemen, but so far GPS-guided drones have been limited to battlefield or southern border patrols and have not been allowed to fly widely in U.S. airspace.

Under pressure from the Pentagon and drone manufacturers, Congress ordered the FAA to write rules allowing government and commercial use of drones on U.S. soil by 2015. The plan could eventually see police drones spying on U.S. cities, drones monitoring power company transmission lines, or GPS-guided freighter-sized drones delivering packages across the country without a driver. FedEx founder Fred Smith said he hopes to add drones to his fleet soon.

The new rules have raised privacy concerns about a "surveillance society" where drones tirelessly monitor our every move 24/7. But Humphreys' experiment puts a whole new spin on anxieties about drones.

"What if you could shoot down one of these drones delivering a FedEx package and use it as your missile?" It's the same mentality as the 9-11 attackers."

This is something the government is acutely aware of. In the deserted desert of the White Sands Missile Range in New Mexico, officials from the FAA and Department of Homeland Security watched Humphrey's team constantly take control of a drone from a remote mountaintop. The results were as dramatic as the test at UT Stadium a few days earlier.

The Department of Homeland Security is trying to identify and mitigate gps jamming with its new Patriot Watch and Patriot Shield programs, but the effort is poorly funded, still in its infancy, and mostly aimed at finding people using jammers rather than spoofers.

The potential consequences of GPS spoofing are simply chilling. Humphries warned that terrorist groups could match his technology and wreak havoc in crowded U.S. airspace.

"I'm afraid they're going to crash into other planes." "I'm worried they're going to crash into buildings. We could have a collision in the air and there could be casualties, so we want to prevent that from happening and fix it."

Unlike military drones, which use encrypted GPS systems, most drones flying over the United States will rely on civilian GPS, which is not encrypted and can be easily infiltrated. Humphreys warned that the government needed to address the loophole before allowing drones widespread access to U.S. airspace.

"It just shows the mindset that we had after 9-11, when we reinforced the cockpit doors to prevent people from hijacking airplanes - well, in terms of the navigation systems of these drones, we need to adopt that mindset."