Cellphone-intercepting 'Stingray' spy technology is being used in the UK

Technology that secretly intercepts and listens to people's mobile phone calls is being used in the UK, an investigation by Sky News has found.

It is not clear who is using the technology or why.

The tech goes by the commercial term "Stingray." It works by mimicking a cellphone tower. However, instead of providing call service or wireless reception, a Stingray simply listens to the call you're currently making via an "IMSI-catcher." IMSI stands for International Mobile Subscriber Identity - a unique number that identifies users on their phone network.

Stingrays are frequently used in the US by local law enforcement to monitor suspects. They have been the subjected of heated debate because Stingrays can listen to anyone's calls, even without a warrant. Because of the way they work, Stingrays hoover up vast amounts of call data from individuals not related to the person being targeted - everyone's call data, basically. The American Civil Liberties Union (ACLU) says Stingrays are "incredibly invasive."

Armed with the technology, the advocacy group says, "law enforcement can - without any assistance or consent from cell phone carriers - pinpoint a person's location in the home, a place of worship or a doctor's office, or conduct mass surveillance on people gathered in an area, whether for a protest, lecture or a party. Even when used to target a particular suspect, Stingrays sweep up information about innocent individuals who happen to be in the vicinity."

UK police forces have long refused to provide information on whether they use Stingray devices. In August 2014, Motherboard published a piece entitled "UK Police Won't Admit They're Tracking People's Phone Calls."

Met commissioner Bernard Hogan-Howe told Sky News that "We're not going to talk about it, because the only people who benefit are the other side, and I see no reason in giving away that sort of thing ... If people imagine that we've got the resources to do as much intrusion as they worry about, I would reassure them that it's impossible."

But Sky has now found that someone is using IMSI-catcher technology in the UK - likely the police. The news service found more than 20 instances of Stingray use in London over a three-week period. The surveillance tech was discovered with the assistance of security company GMSK Cryptophone, which has previously helped track down instances of Stingray use in the US.

The Times and the Guardian have both previously reported that UK police have paid for and are using Stingray tech - but Sky says this is "the first direct evidence of Stingray use in the UK."

Of course, it's also possible that it's not the police using Stingrays - or not just the police. The tech doesn't require the cooperation of cellphone or telecoms companies to intercept the calls. So it's conceivable that a rogue third-party could - with the right technical expertise - build their own IMSI-catcher.