How Vulnerable Is G.P.S.?

In the cool, dark hours after midnight on June 20, 2012, Todd Humphreys made the final preparations for his attack on the Global Positioning System. He stood alone in the middle of White Sands Missile Range, in southern New Mexico, sixty miles north of Juárez. All around him were the glowing gypsum dunes of the Chihuahuan Desert. On a hill about a kilometre away, his team was gathered around a flat metal box the size of a carry-on suitcase. The electronic machinery inside the box was called a spoofer--a weapon by another name. Soon, a Hornet Mini, a drone-operated helicopter popular with law-enforcement and rescue agencies, was scheduled to appear forty feet above them.