With all the spying, hacking and digital theft going around in the past couple of years, you'd think people would be more cautious, especially GCHQ, which has a pretty tight grip on all communication moving around the UK.
It seems the reality is quite different. Someone managed to bypass the switchboard security and was given the mobile phone number of the head of GCHQ, Sir Robert Hannigan, V3.co.uk reports.
As Mr. Cameron later explained, the prank call took place on Sunday morning, while he was out for a walk. Somebody told him (presumably a government switchboard operator, V3 says) that he was being put in a conference call with Hannigan.
At the start of the call, the caller apologised to Cameron for ‘waking him up’. It was 11am on Sunday, and that was immediately suspicious to Cameron. "I thought that was strange as it was eleven o'clock in the morning," Cameron said.
He then asked the hoaxer to identify himself, as he didn’t recognise his voice. The caller then said it was a prank call and hung up. Cameron said there was "no harm done... no national security breached”, BBC reports.
A government spokeswoman said a notice has gone out to all departments to be on the alert for hoax calls following the incident.
She said: "The prime minister ended the call when it became clear it was a hoax. In neither instance was sensitive information disclosed.
"Both GCHQ and Number 10 take security seriously and both are currently reviewing procedures following these hoax calls to ensure that the government learns any lessons from this incident."