The Critical Hole at the Heart of Our Cell Phone Networks

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SS7, also known as Signaling System No. 7, refers to a data network—and the series of technical protocols or rules that govern how data gets exchanged over it. It was designed in the 1970s to track and connect landline calls across different carrier networks, but is now commonly used to calculate cellular billing and send text messages, in addition to routing mobile and landline calls between carriers and regional switching centers. SS7 is part of the telecommunications backbone but is not the network your voice calls go through; it’s a separate administrative network with a different function. Think of it like a passenger train system—SS7 is the maintenance tunnels workers use rather than the main tunnels through which passenger trains travel.

To track you, an attacker could send what’s called an Anytime Interrogation request to your carrier to get the unique ID of your phone and identify which mobile switching center (MSC) your phone uses—usually one MSC covers an entire city. Carriers use this information to determine your location to route your calls and messages through the cell tower closest to you. By sending repeated Anytime Interrogation requests to get this and your GPS coordinates, an attacker can track your phone, and you, to the street block where you are standing, using Google maps


The Critical Hole at the Heart of Our Cell Phone Networks