AUSTIN, Texas — After a dress rehearsal at Royal-Memorial Stadium, University of Texas researchers traveled to New Mexico last month and demonstrated for U.S. Department of Homeland Security officials how an unmanned aerial vehicle, or drone, can be commandeered by hacking into its navigation system.

The technique, known as spoofing, created false Global Positioning System signals that tricked the drone’s GPS receiver into steering a new course.

The GPS, which uses satellites and radio signals, is not encrypted for civilian uses, and that raises concern about the federal government’s plan to permit thousands of drones in U.S. air space for commercial, law enforcement and university purposes, said Todd Humphreys, an assistant professor at the university’s Cockrell School of Engineering.

“The dirty fact is it’s an open signal, and easily hacked,” Humphreys said.

Well, maybe not easy for just anyone to hack. Although Humphreys and his students built their spoofing device for about $1,000 in off-the-shelf hardware, it took three Ph.D. students four years to write the software.

The hacking June 19 at White Sands Missile Range in New Mexico is “the first known unequivocal demonstration” that commandeering a drone via GPS spoofing is technically feasible, the engineering school said on its website. The test was performed using a civilian drone owned by the university.

Humphreys and his students knew they had nailed the technique five days earlier, during a trial run at the football stadium. Humphreys had originally planned the test for a field at the University of Texas’ Pickle Research Campus in North Austin. But looking out his office windows at the stadium, he figured “maybe there’s a chance.” Officials in the athletic department and in university President Bill Powers’ office signed off. The football team’s strength training practice was moved to accommodate the test.

Humphreys, who said he had regarded the stadium as “ugly and a gargantuan waste of money,” said athletic officials were “wonderful. They even brought out Gatorade and a tent for us.” The dress rehearsal went well. The drone, which looks a bit like a miniature helicopter that would fit on a kitchen table, hovered above the field until students sent counterfeit GPS signals that tricked it into “thinking” it was rising. That caused the drone to drop sharply. At White Sands, the team took control of the hovering drone from a little more than half a mile away.

Humphreys said the Global Positioning System needs to be fortified with “electronic watermarks” that would make its signals much harder to falsify. That would cost millions of dollars, he said. Military GPS signals are encrypted and effectively unspoofable, he said.

The Department of Homeland Security, which invited the university to conduct the test at White Sands, referred a request for comment to its Customs and Border Protection unit. Spokesman Michael Friel said that sort of hacking would not affect the security of its drones.