The stolen SIM keys don’t just give the NSA the power to listen in on calls, but potentially to plant spyware on any phone at any time. Once the stolen keys have bypassed the usual protections, the spyware would live on the SIM card itself, undetectable through conventional tools, able to pull data and install malicious software. If the NSA and GCHQ are pursuing that capability, it could be one of the biggest threats unearthed by Snowden so far.
