Since 2008, the Justice Department has been using license plate scanners to track millions of cars in real-time around the U.S. as part of a massive domestic intelligence-gathering program that's largely been kept secret. It's like PRISM for cars and we have no idea how big it is The program, run by the Drug Enforcement Administration, was originally developed as a way to monitor vehicles used for drug trafficking, but the database is now employed by both federal and local authorities to track people accused of everything from rapes and murders and as part of the Amber Alert system.

According to a report by the Wall Street Journal, at least 100 cameras were feeding information into the database back in 2011 which:

…collects data about vehicle movements, including time, direction and location, from high-tech cameras placed strategically on major highways. Many devices also record visual images of drivers and passengers, which are sometimes clear enough for investigators to confirm identities…

The program was originally limited to border states, including Arizona, California, Nevada, New Mexico, and Texas to crack down on drug trafficking, but it's expanded at a rapid clip. Officials wouldn't say how many cameras are now feeding data into the system or what other states are contributing to the national database because "disclosing such information could help criminals avoid detection."

Documents obtained by the WSJ show that the DEA is also tapping into license plate readers operated by both state and local law enforcement to expand the size and scope of the database, and in one email from 2010, that the program was primarily used for asset forfeiture The document said, "…DEA has designed this program to assist with locating, identifying, and seizing bulk currency, guns, and other illicit contraband moving along the southwest border and throughout the United States. With that said, we want to insure we can collect and manage all the data and IT responsibilities that will come with the work to insure the program meets its goals, of which asset forfeiture is primary."

While the program began in 2008, it was opened to state and local authorities the next year. The data is stored at the El Paso Intelligence Center in Texas – known as EPIC in law enforcement circles – and any participating police agency can request data around the clock.