German researchers have discovered security flaws that could let hackers, spies and criminals listen to private phone calls and intercept text messages on a potentially massive scale – even when cellular networks are using the most advanced encryption now available.

The flaws, to be reported at a hacker conference in Hamburg this month, are the latest evidence of widespread insecurity on SS7, the global network that allows the world’s cellular carriers to route calls, texts and other services to each other. Experts say it’s increasingly clear that SS7 is riddled with serious vulnerabilities that undermine the privacy of the world’s billions of cellular customers.

A secret message was delivered to the National Security Agency. An intelligence unit within the U.S. military’s Africa Command needed help to hack into Libya’s cellphone networks and monitor text messages. For the NSA, the task was easy.

The agency had already obtained technical information about the cellphone carriers’ internal systems by spying on documents sent among company employees, and these details would provide the perfect blueprint to help the military break into the networks. The NSA’s assistance in the Libya operation, however, was not an isolated case. It was part of a much larger surveillance program.