The US Justice Department has been accused of using technology on planes that can mimic cellular towers and fool smartphone users into believing they're connecting to a genuine phone network.

Dubbed 'dirtboxes', the spy tool will apparently collect unique information about connected devices to track certain suspects without requiring any help from networks. That's according to a report by the Wall Street Journal (WSJ), which claims the system grabs all information from mobile phones that it can in order to pinpoint one subject.

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"Interceptor use in the U.S. is much higher than people had anticipated," said Les Goldsmith, the CEO of ESD America. He told Popular Science, "One of our customers took a road trip from Florida to North Carolina and he found eight different interceptors on that trip. We even found one at South Point Casino in Las Vegas." He added, "What we find suspicious is that a lot of these interceptors are right on top of U.S. military bases. Whose interceptor is it? Who are they, that's listening to calls around military bases? The point is: we don't really know whose they are."