The rioters causing havoc on British streets have eschewed traditional social networking sites as a way of organising, instead using the encrypted instant chat service on their BlackBerry handsets.
Although BlackBerrys are normally associated with white-collar workers keeping up with their emails, they are used by 37 percent of young adults and children in Britain, according to recent industry figures.
They are popular because the BlackBerry Messenger (BBM) service offers a free alternative to texting and can send messages to many people at once. It is also encrypted, unlike Twitter which was used by protesters in Iran and Egypt.
"If you use Blackberry Messenger it's usually just you or your local group of contacts you've personally approved who can see your messages. That's why they've been preferring to use it," said Alastair Paterson, chief executive of cybersecurity firm Digital Shadows.
He said social media had proved "a very efficient tool for communicating, being able to effectively outwit the police by very quickly allowing them to move between areas that they know the police haven't been to yet".
"So before the police can show up they're already able to go in, do the damage and escape," Paterson told AFP.
David Lammy, an opposition lawmaker for the north London borough of Tottenham where the riots began on Saturday night, has urged BlackBerry to consider temporarily suspending the messenger service to stop youths using it to organise.
It was "one of the reasons why unsophisticated criminals are outfoxing an otherwise sophisticated police force," he wrote on Twitter on Tuesday, shortly before a fourth night of violence erupted in British cities.
Messages have been sent out to teenagers across the country calling for rival gangs to unite in the destruction, and for rioters to target police, according to messages published by the Daily Mirror newspaper.
One broadcast on Sunday, the first night the violence spread beyond Tottenham, said: "Everyone from all sides of London meet up at the heart of London (central) OXFORD CIRCUS!! Bare SHOPS are gonna get smashed up so come get some."
It continued: "If you see a brother... SALUT! if you see a fed... SHOOT!"
That evening about 50 youths attacked Oxford Circus, on the famous Oxford Street shopping avenue in central London.
BlackBerry has offered any help it can to the authorities in Britain.
"We feel for those impacted by recent days' riots in London. We have engaged with the authorities to assist in any way we can," said Patrick Spence, managing director of global sales and regional marketing for BlackBerry.
"As in all markets around the world where BlackBerry is available, we cooperate with local telecommunications operators, law enforcement and regulatory officials," he added.
The Canadian firm which makes BlackBerry, Research in Motion (RIM), was threatened with reprisals on Tuesday if it released BBM messages to the British authorities.
"If you do assist the police by giving them chat logs, GPS locations, customer information and access to peoples' BlackBerry Messengers, you will regret it," said a message posted on RIM's official blog.
It warned that a hacked database containing contact details of RIM employees would be made public and "passed onto rioters", adding: "Do you really want a bunch of angry youths on your employees' doorsteps? Think about it."
A BlackBerry source confirmed that it has yet to suspend the BBM service, and Paterson from Digital Shadows said that such a move would not stop the rioters.
"If you shut it down you just displace that behaviour to other services. Blackberry is not the only closed messaging system," he told AFP.
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