The Wall Street Journal is reporting that the federal government has a secret, airplane-based surveillance system that is capable of sweeping up information from thousands of cell phones at a time. While the device is intended to spy on criminal and terrorist suspects, the program also sweeps up private information from many innocent people. The Justice Department says the program complies with the law and is subject to judicial oversight, but some civil libertarians are skeptical.

How the program works

When you turn on your cell phone, it immediately puts out a call to find the nearest cell phone tower. Ordinarily, it will connect with a cell phone owned by your service provider.

But the Department of Justice has a fleet of airplanes outfitted with special hardware that can trick phones into connecting to the airplane instead of a conventional cell phone tower. Because each cell phone has a unique identifier, this registration process can help the feds determine who owns the phone and track a suspect as he moves from location to location.

The technology is designed to minimize disruption, but according to the Wall Street Journal, it's not perfect. When the plane flies overhead, it can disrupt some phone calls that are in progress.

It has long been known that law enforcement has the ability to spy on cell phones using fake towers. But in the past, the public only knew about ground-based systems that only operated over a limited area. The airborne devices reported by the Journal can capture cell phone signals over a much wider area, increasing the potential for capturing the communications of innocent people.

Why civil libertarians are concerned

Officially, this program is focused on tracking the location of criminal and terrorist suspects. But the way it works means that other peoples' information will be swept up as well.

If the government immediately deleted information collected "incidentally," that might not be a problem. But in recent years we've learned that the feds take just the opposite approach: a number of programs have warehoused information about non-suspects, in the hopes that it would prove useful for subsequent investigations.

Over time, the government could accumulate large volumes of private information about Americans who are not suspected of any crime — all without judicial oversight. Civil libertarians believe there should be stricter rules to prevent this from happening.