GCHQ also claimed the ability to manipulate the billing servers of cell companies to “suppress” charges in an effort to conceal…

“GCHQ also claimed the ability to manipulate the billing servers of cell companies to “suppress” charges in an effort to conceal the spy agency’s secret actions against an individual’s phone. Most significantly, GCHQ also penetrated “authentication servers,” allowing it to decrypt data and voice communications between a targeted individual’s phone and their telecom provider’s network. A note accompanying the slide asserted that the spy agency was “very happy with the data so far and [was] working through the vast quantity of product.””

–The Great SIM Heist: How Spies Stole the Keys to the Encryption Castle (viaiamdanw)