In an interview with the BBC, the whistleblower said British spies can hack phones with a simple text message and make audio recordings or take photos without owner’s knowledge, Geo Tv reported on Tuesday.
Snowden did not say either of the Government Ccommunications Headquarters or the National Security Agency were interested in mass-monitoring of citizens’ private communications.
Both the agencies had heavily invested in technologies to hack smartphones, he said.
Snowden said GCHQ used a series of interception tools called “Smurf Suite”, after the blue cartoon characters, The Smurfs.
“Nosey Smurf” enabled spies to switch on a smartphone’s microphone even if the phone was off, he said.
He said the text message sent by GCHQ to gain access to the phone can not be noticed.
The BBC said the UK government declined to comment in line with usual policy on intelligence matters.
Snowden, has been charged by the US with espionage and theft of government property after he leaked documents about digital espionage. He lives in Russia since June 2013.