Scotland Yard foiled riots on the Olympics site by monitoring "chitter chatter" on Twitter and BlackBerry Messenger.
Police chiefs also considered seeking powers to shut down Twitter on a temporary basis amid concern about social networking websites' role in last week's crisis, MPs were told.
Attacks on Oxford Street and the two Westfield shopping centres in east and west London were averted as detectives scoured the mobile phones of people arrested during the riots, officers said.
Assistant Commissioner Lynne Owens told MPs on the Commons Home Affairs Select Committee there was so much traffic on Twitter and BlackBerry Messenger (BBM) that at times the Met was overwhelmed.
"There was intelligence that the Olympic sites, that both Westfields and Oxford Street were indeed going to be targeted," she said
"We were able to secure all those places and indeed there was no damage at any of them.
"All those locations were protected and we were able to respond because of our live-time monitoring of Twitter and BBM."
Asked about Twitter's role during the escalating violence in London, Acting Commissioner Tim Godwin told the committee: "I contemplated seeking the authority to switch it off. The legality of that is very questionable and additionally it is also a very useful intelligence asset.
"The only problem with it is it's a massive amount of information that you need to synthesise and some of it is quite obviously wrong and rather silly.
"As a result of that we did not request that that was turned off but it is something we are pursuing as part of our investigative strategy."