They can be slipped into a suitcase and used almost anywhere to spy on mobile phone communications. IMSI catchers are high-tech portable devices used by law enforcement agencies across the world to secretly intercept conversations and text messages. But could they be abused for criminal purposes? The answer is yes, according to an alarming report from Europe last week.
Czech broadcaster Radio Prague revealed that the use of IMSI catchers is on the rise in the country—but not by the authorities. A senior police chief, Tomas Almer, told the station that police had been detecting unauthorized IMSI catchers (called agátas in Czech) being used across the country, though had not been able to catch any of the perpetrators. Why use an IMSI catcher if you aren’t hunting for bad guys? Former Czech intelligence agency chief Andor Sandor said that businesses could be using them to spy on one another. And, as Radio Prague suggested, it’s possible that criminal gangs could be using them for extortion.
IMSI catchers are advanced pieces of hardware that can be used to send out a signal, tricking mobile phones into thinking they are part of a legitimate mobile phone network. The most sophisticated IMSI catchers, such as the one known to have been purchased by London’s Metropolitan Police, allow authorities to shut off targeted phones remotely and gather data about thousands of users in a specific area. They can force phones to release their unique IMSI and IMEI identity codes, which can then be used to track a person's movements in real time.
The use of the technology by police—let alone criminals—is controversial. Recently, some argued that the FBI’s use of an IMSI catcher known as a “Stingray” was unconstitutional under the Fourth Amendment, which prohibits unreasonable searches and seizures. Until November last year, the Department of Justice had claimed the use of a Stingray did not constitute a search. However, the DoJ suddenly changed tack during an Arizona court case, a move the Wall Street Journal reported was “designed to protect the secrecy of the gadgets.”
Largely due to the endemic scale of that secrecy, little is known about how widely IMSI catchers are being used. It is highly likely that most modern police forces, especially those in densely populated cities where there are fears about terrorism and other serious crime, will have one or two in their possession. Perhaps of greater concern, though, in some places, tech-savvy criminals could be deploying their own cut-price IMSI catchers. As hacker Chris Paget illustrated in 2010, while police-grade versions of the technology can cost hundreds of thousands, for about $1,500 it’s possible to design a DIY IMSI catcher, which could be used for all sorts of nefarious purposes.
More details about the use of the spy tools may soon emerge, as civil liberties groups like the ACLU continue to demand transparency from U.S. authorities on issues related to phone tracking and surveillance. In London, the group Privacy International has gone one step further, taking action into its own hands in a quest to track down users of the technology. PI has hatched a rather ingenious plan, investing earlier this year in what it calls an “IMSI catcher catcher”—a device designed to snoop on the snoopers, sniffing out anyone operating an IMSI catcher in a given location.
In the meantime, if you’re concerned about an IMSI catcher eavesdropping on you—whether it’s being wielded by law enforcement or by criminals—there is, unfortunately, no simple solution. You could invest in encryption software for yourself and your friends. Failing that, well, you could always just stop using your phone.