“Dear subscriber, you are registered as a participant in a mass disturbance.” That's the chilling text message people near the clash between Ukrainian riot police and protesters in Kiev yesterday received shortly after midnight, Andrew E. Kramer at the New York Times reports.

The protests were in response to new restrictions on speech and assembly rights signed into law by President Viktor Yanu­kovych. Those laws followed public protests brought on by Yanukovych's decision not to sign a free trade agreement with the European Union. The language in the text message mirrors a law that makes it a 3crime punishable by jail time to participate in a protest that is deemed violent, according to Kramer.

As eerie as the text message may seem, it was likely not technically difficult to achieve. Presumably, authorities could determine who was in the vicinity of the protest by going through the records of nearby cell towers. In the United States, that type of information can be requested from mobile providers in the form of "tower dumps" which reveal the locations of hundreds or thousands of innocent citizens associated with a specific cell tower, along with suspects. A recent congressional inquiry shows that U.S. law enforcement made more than 9,000 requests for tower dumps in 2012.

Cell site location data is considered metadata. The U.S. government denies that it is currently tracking mobile phone locations domestically, although it admits to running a test project on the subject in recent years. And documents leaked by former National Security Agency (NSA) contractor Edward Snowden show the NSA tracks 5 billion mobile device locations daily around the world.

"This incident highlights how location metadata — contrary to NSA defenders' claims that such data isn't sensitive — is incredibly powerful, especially in bulk, and can easily be used by governments to identify and suppress protesters attempting to exercise their right to free expression," says Kevin Bankston, policy director for the New America Foundation’s Open Technology Institute.

Yet despite what appears to be an attempt to use the geolocation technology built into cellphones to clamp on dissent, Kramer reports that the text messages had little effect on the ongoing protests in Kiev. "Three hours after it was sent," he wrote, "the riot police pushed past barricades of burned buses on Hrushevskoho Street near Parliament but were nonetheless met by a crowd of protesters in ski masks and helmets carrying sticks and ready to fight."