By Daniel Emery
Technology reporter, BBC News
The foreign secretary said there was no security risk posed by knowing John Sawers wore Speedos
The perils of putting personal data on Facebook were made painfully obvious when the wife of John Sawers - the next head of MI6 - put details, photos, and information about him and his family on the social networking site.
Lady Sawers revealed the location of the London flat used by the couple, the whereabouts of their three grown-up children and the address of Sir John's parents.
There were also photographs of the future spy chief on the site, forcing the Foreign Secretary, David Miliband, to do a tour of TV studios, saying: "You know he wears a Speedo swimsuit. That's not a state secret."
According to IT security firm, NCC Group, UK intelligence agencies are concerned that Facebook and other social networking tools are "ruining" the spy industry, as finding new recruits without an online trail becomes nearly impossible.
But is that the case? The question was put to Crispin Black, a former intelligence officer for both the Ministry of Defence and the Cabinet Office and ex-intelligence analyst with the Joint Intelligence Committee.
"In the old days, you would take any incriminating photos or files and lock them in the attic," he said.
"These days it is more difficult; it's not unusual for people to do things at university, perhaps while drunk, and for someone to take a snap on a mobile phone and upload to the internet."
Mr Black says that old photos are not such a huge problem as a person's look and habits of dress change over time. Recent photos, especially if you're a field operative, would not be good but, says Mr Black, that rarely happens.
"Providing you front up during the vetting process, it usually doesn't matter. They will then know what sort of person you are.
"What they usually say is if any of these people [ex-girlfriends etc] ever get in touch with you or start to cause trouble, then just tell us," he said.
Once you are in the service, personnel have to be discreet about their work. No-one ever says they work for MI5 or MI6; agents instead say they work for the Ministry of Defence or Foreign Office respectively, although they are allowed to tell their close family the truth.
So if the rules on operatives - once they are in the service - keeping a low presence online are clear, why would the wife of a very senior spy put personal details on a social networking site without any privacy measures?
Mr Black says the problem for Mr Sawers' family was that they had been living in diplomatic circles for almost 20 years.
"Mr Sawers was an ambassador for Egypt, which makes him a very public figure.
There are worries that photographs taken by troops in Afghanistan could be used by the enemy to gain information
"But life in the intelligence services is a more secret world and once in they have to keep a low profile, although these days you don't need to live a double life.
"The stuff on the beach is harmless, but the Facebook entry also had address and personal information and that is a very different thing," said Mr Black.
Mr Black said there could well be people - from foreign agents to home-grown lunatics - who might "want a pop at C" the name the head of MI6 is given (the director general of MI5 has not been known by the soubriquet "K" since the 1940s.).
By giving away information, in this case the address of Mr Sawers parents and his children, that could enable someone to threaten Mr Sawers or his family.
"Stella Rimington did a similar thing once," said Mr Black. "She had to be relocated for her own protection.
"Cock-ups happen, but when it comes to security the bill comes to the taxpayer.
"Relocating someone from an address in Chelsea isn't cheap and the national mood at present is that we're under financial pressure, so things like this do not help."
A more serious problem, said Mr Black, was when soldiers serving in Afghanistan or Iraq posted photos or videos to social networking sites.
"Snaps or film taken by serving forces could reveal vulnerable locations in a base, while a Twitter line could provide information to the enemy.
"In the old days, this was the sort of stuff the IRA would kill for, today an enemy could scan some photos and gain an insight into a base," said Mr Black.
"And that poses a real security headache."