REUTERS/Mark Blinch
Snowden told the BBC that GCHQ has something called "Smurf suite," which is a collection of spying programs that the agency can use to hack into the phones of suspected terrorists.
One tool is called "Dreamy Smurf." Snowden says it allows GCHQ to turn on mobile phones without the user knowing. There's also "Nosey Smurf," which can be used to turn on the phone's microphone.
Another tool in GCHQ's "Smurf suite" is "Tracker Smurf." It can turn on a smartphone's geolocation feature, which allows intelligence agencies to accurately track a user's location. Authorities can already track smartphones by measuring which cell tower they're nearest to, but it looks like this tool is much more accurate.
One GCHQ program isn't about spying at all. It's called "Armoured Smurf." If a user suspects that something is wrong with their phone and tries to inspect it, then it hides GCHQ's spy software.
Snowden explained that GCHQ gains access to smartphones with a simple text message. "It's called an 'exploit'," he said. "That's a specially crafted message that's texted to your number like any other text message but when it arrives at your phone it's hidden from you. It doesn't display. You paid for [the phone] but whoever controls the software owns the phone."