The Defence Secretary has criticised NATO for not being "agile" enough to prevent Russian cyber attacks on Europe.
Speaking on the first day of the annual Security Conference in Munich, Sir Michael Fallon said the alliance has work to do and would not say whether or not the UK was carrying out offensive cyber attacks against Russia.
"The NATO machinery is not geared up," he said.
"It has not been fast enough in dealing with threats like terrorism or cyber.
"That's one of the areas in which NATO needs to be more agile. It needs to respond to cyber threats.
"Cyber capabilities are obviously sovereign and belong to the nation states, the member states of NATO. But NATO needs to get sharper about how those (capabilities) could be deployed in the NATO context and how we deter against cyber threats. That is a role for NATO."
At last summer's NATO Summit in Warsaw, leaders agreed that a cyber attack could constitute an Article Five response, raising the prospect of war if an enemy state hacked a NATO country.
Pressed by Sky News on what that could mean, Sir Michael would not give details.
"We are very careful about not articulating exactly how and Article 5 would be defined or calibrated because that would only give comfort to our adversaries," he said.
"It's very important that we remain uncertain as to how NATO would respond."
Privately it is felt that any attack would have to result in the loss of life before Article 5 was triggered, but in the past year Russia has been openly accused by governments of interfering in the US elections and there are fears it is doing the same in the forthcoming French and German votes.
NATO does has a Cyber Centre of Excellence in Tallinn, Estonia, but there is no centralised NATO cyber framework.
Recently the alliance formally recognised cyber as a 'domain' alongside land, sea and air, but the organisation continues to prioritise its traditional military response despite a hybrid campaign being waged by Moscow.
Sir Michael said: "We now need to work on cyber deterrence and how we deter cyber attacks and then on how we use national cyber capabilities for the good of NATO.
"It's a very good example of where NATO needs to be more agile."
(c) Sky News 2017: Fallon: NATO failing to stop Russian cyber attacks