'It would be very difficult to know whether the phone has been compromised.'

London - Spies can eavesdrop on people through their smartphones even if owners think the device is switched off, experts claim.

British and US spooks have access to software which can activate the microphone on a target’s mobile phone, allowing them to listen to conversations.

Security experts said phones can appear to be shut down, but really be on a low-power mode with the communication chips active for spies to use.

This “playing dead” trick means the phone can receive commands, such as a request to turn on its microphone.

The technique was revealed by National Security Agency (NSA) whistleblower Edward Snowden during an interview with an American news network. He claimed the technique is being used by the NSA in the US and its British equivalent, GCHQ.

Asked if spies were able to operate someone’s phone remotely, he replied: “As soon as you turn it on, it can be theirs. They can turn it into a microphone. They can take pictures from it. They can take data off of it. Even turning a phone off doesn’t stop it.”

Eric McDonald, a hardware engineer in Los Angeles, confirmed the snooping technique was possible, saying:”‘It would be very difficult to know whether the phone has been compromised.”

* A security flaw has been found in Apple’s iOS 7 operating system which could allow millions of iPhones and iPads to be hacked.

A Canadian technology expert discovered a series of steps which can bypass a device’s lock screen, meaning it can be accessed without putting in a security code. - Daily Mail