Intelligence agencies should track social networking sites more closely, the UK's top civil servant has said.
Sir Gus O'Donnell told the Iraq inquiry that events in Egypt, where protests against the government are escalating, showed the value of "open source" intelligence as a barometer of opinion.
The issue would be examined as part of a review of government intelligence "machinery" due by the summer, he said.
But he said any information gathered must, above all, be "reliable".
Sir Gus, who has been cabinet secretary and head of the Civil Service since 2005, was questioned about the UK's current intelligence-gathering methods during his evidence to the Chilcot Inquiry into the 2003 Iraq invasion.
He was asked whether the Joint Intelligence Committee - which assesses raw material picked up by intelligence officers in the field and presents it to ministers - was able to "pick up" on popular protests organised through Facebook, Twitter and other social media.
"When you look at what is happening, as we speak, in Egypt... the use of the internet, the use of Twitter, the way protest movements develop, this is a different world," he said. "We need to be tied in much more to that sort of world."
Sir Gus, who attends weekly meetings of the National Security Council established by David Cameron, suggested the UK needed to go a "bit further" in this area to get a fuller picture of fast-moving, volatile situations when they emerge.
As well as the current demonstrations in Egypt, he cited the mass protests in Iran following the disputed 2009 presidential election as evidence that the internet has "profoundly changed" how protest movements form. "Individuals can come together in a way that in the past was more difficult," he said.
There was a "massive amount" of information that was freely available, Sir Gus stressed, and the government's listening post GCHQ had an important role to play in "bringing this all together".
"I have strongly and always been of the view that we probably underestimated open source [intelligence]. By its nature, the secret agencies tend to want to push the secret stuff. One of the questions I will be asking is, are we tapping into all of the best available information that is out there in an open sense?"
But the sheer amount of information being passed around placed an even greater burden on ensuring its credibility, he stressed.
"The problem is that there is too much information. The issue is being able to find the things you need without being swamped which the things that are irrelevant... and then understanding the reliability of that information."
No 10 and the Cabinet Office have launched a review of the government's intelligence machinery to ensure it is working at its "maximum effectiveness".
Issues to be looked at include the relationship between the Joint Intelligence Committee and the National Security Council, how intelligence assessment is aligned to strategic security priorities and how to ensure ministers get appropriate intelligence at the right time.
The review, to be conducted by the national security adviser and the chairman of the Joint Intelligence Committee, is expected to be completed by the summer with a summary of findings made public.