Billions could have their mobile phone calls intercepted and recorded after computer hackers cracked the secret code used to protect 80 per cent of the world’s users.

The code was posted on the internet by German scientist Karsten Nohl, who said he organised the breach to demonstrate the weakness of mobiles’ security measures.

He claims an eavesdropper could be listening to calls within 15 minutes with just a laptop and two network cards.

There are now fears that half the world’s population could be left vulnerable to crime including identity fraud.

Nohl said: ‘We have given up hope that network operators will move to improve security on their own, but we are hoping that with this added attention, there will be increased demand from customers for them to do this.

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