Users of social media are constantly warned to watch what they reveal online. You never know who might read your postings, the argument goes — your grandmother, your boss, potential employers.
To that list of potential readers, you'll have to add the police, at least if you live in Britain.
Wired UK reports that London's Metropolitan Police, or Scotland Yard in popular parlance, has admitted the existence of a team dedicated to monitoring the social media postings of some 9,000 people for signs of political unrest.
The unit has 17 officers and uses what it calls Social Media Intelligence, or SocMint, to scan Facebook, Twitter, YouTube and other social media services 24 hours a day, Wired UK said, adding that the team is developing special tools to smooth the process.
As part of the Metropolitan Police, the unit has jurisdiction in all of England and Wales, and some jurisdiction in the legally distinct "countries" of Scotland and Northern Ireland.
At a security conference in Australia last month, a Scotland Yard official, Umut Ertogral, spoke freely during what he thought was a closed-door meeting.
Social media "almost acts like CCTV [closed-circuit television] on the ground for us, really," Ertogral said, according to the Australian Financial Review.
Etrogral is head of open-source intelligence at Scotland Yard's National Domestic Extremism Unit (NDEU), which means that his team mines publicly available information for home-grown British terrorists, fringe groups and politically motivated troublemakers.
Through a freedom-of-information request, the Guardian learned that the NDEU currently keeps track of at least 8,931 Britons suspected of being "domestic extremists."
"When there's a protest, people go out and record video, and we know two minutes later they'll be on YouTube," Etrogral reportedly said at the Australian conference. "And because people on the Internet are very silly, they'll say 'That's my mate Joe Bloggs.'"
A spokesman for the Metropolitan Police confirmed the existence of the social-media unit to Wired UK, adding that it was necessary to "uphold the law and prevent and detect crime."
Some American police do the same thing, though perhaps less systematically. The New York City police department monitors the Facebook pages and Twitter postings of suspected gang members and juvenile petty criminals in case something incriminating gets posted — and it often does.
All of this is perfectly legal. It's using only data that people have already made public. In a way, it's no different from Googling the name of someone you've just met.
Not everyone, however, sees it that way.
"The perception with this kind of intelligence is that it's in the public domain, so it's no different from, say, searching through newspaper articles," Daniel Trottier, a researcher at the University of Westminster in London, told Wired UK.
"But this analysis shows a lack of familiarity with the technology involved," Trottier added. "With just a few statements from social media profiles, one is able to reasonably determine a user's sexual orientation," among other possibly private details.
Once again, the adage comes up — if you don't want your grandmother to see it, you don't want the police to see it either.