Security experts have revealed that they received suggestions of a cyber attack targeted at the opening ceremony of last summer's Olympic Games.
Oliver Hoare, head of cyber security for the Games, told the BBC he received a phone call from government listening post GCHQ on the day of the opening ceremony.
There were concerns that the lights in the Olympic stadium could have been turned off during the ceremony.
The threat failed to materialise and the ceremony went off without a hitch, but security officials revealed that they had put extensive precautions in place to withstand such an attack.
"There was a suggestion that there was a credible attack on the electricity infrastructure supporting the Games," Hoare told the BBC.
"And the first reaction to that is, 'Goodness, you know, let's make a strong cup of coffee and get into the office'."
Hoare said that extensive testing had taken place to mitigate a wide range of attacks, including the exact scenario that raised concerns on the first day.
He said: "We'd tested no less than five times the possibility of an attack, a cyber attack, on the electricity infrastructure.
"In a sense I think we felt pretty well prepared, but there's always an amount of concern, particularly when you've only got eight or nine hours before the opening ceremony."
Government, Olympic organiser Locog and service providers such as BT were all part of a team that responded to such threats.
The primary response to the threat came from the Olympic Cyber Co-ordination Team (OCCT), based at MI5 headquarters in Thames House.
This involved assessing how credible the threat of attack might be, a process which took place while officials put in place a contingency plan in case the attack was carried out.
"The clock was absolutely ticking," Hoare told the BBC.
"We effectively switched to manual, or had the facility to switch to manual. It's a very crude way of describing it, but effectively we had lots of technicians stationed at various points."
He said that so much resilience in terms of power had been put into place so that "if all the lights went out in east London you could guarantee that the Olympic Stadium would still be burning brightly".
At a Cabinet meeting in the afternoon before the ceremony contingency plans were discussed and ministers informed of the issues, and officials became increasingly confident that they could deal with the threat if it occurred.
Hoare was told an hour before the ceremony by a colleague that "if the lights go down we can get them up and running regardless within 30 seconds", a reassurance that did not quite succeed.
"Thirty seconds at the opening ceremony with the lights going down would have been catastrophic in terms of reputational hit," Hoare said. "So I watched the opening ceremony with a great deal of trepidation."
The attack failed to materialise, but Hoare said he twitched every time the lights in the stadium dimmed as he watched the ceremony at home with his family.
He said: "You wouldn't be human if you didn't have butterflies."
David Harley, senior research fellow for ESET, commented:
"The nature of the threat in these reports isn’t entirely clear, or how much substance there was behind those fears of a direct attack on UK power utilities or the Olympic Games in general, but the business world in general might learn something about risk assessment and contingency planning from this report."