A significant number of cell towers in the US are not what they seem to be. In fact, at least according to a recent report, it’s likely they are snooping on your calls.

One of the impressive things about GSM is that despite being a standard that was devised nearly a quarter of a century ago, it’s still pretty secure. If you’re looking to listen into calls, it’s actually much easier to just switch off the encryption. Les Goldsmith, the CEO of ESD America, which sells a security-hardened phone, says he has found a number of cell sites which do exactly this.

Goldsmith told the US publication Popular Science that he knew of 17 mobile phone towers which forced his phone to 2G and then switched off the encryption. He dubs these as “interceptors” on the basis that they might be running man-in-the-middle attacks where the rogue tower takes a call, siphons it off for interception and also passes it on to the legitimate network.