The Department of Homeland Security wants to build a massive database of information collected from license-plate scanners across the country.

In an advertisement soliciting bids to build the database, Homeland Security said the information would help catch "criminal aliens and absconders." Privacy advocates worry such a database will also ensnare the rest of us.

License plate scanners have become controversial because they don't only record location data of criminals or assorted absconders. They collect data on every license plate that passes. With enough data, those with access can map the habits of ordinary citizens.

"The reason people want to gather that information is because they want to track your movements, and where people go can reveal a great deal about them," said Catherine Crump, a staff attorney with the American Civil Liberties Union. It could track, "where you go to the doctor, your therapist, your church, your gun range, your daily routine. ... So I think Americans have good reason to be concerned about the DHS proposal."

The proposal comes at a time that many Americans are already wary of government intrusion into their personal lives. Courts are currently debating whether the National Security Agency can continue collecting the everyday phone records of millions of citizens.

Department of Homeland Security officials did not return a phone call seeking comment on the database proposal Wednesday, and the contract solicitation did not specify how data would be protected, how it would be stored or for how long it would be maintained.

The database would track vehicle license plate numbers that either pass through cameras or are manually entered into the system. The information would be shared with law enforcement. It also would include a "target vehicle" feature that would allow the agency to upload at least 5,000 license plate records at a time.

Details of the database proposal were first reported by The Washington Post.

U.S. Immigration and Customs Enforcement, which is an agency within the Department of Homeland Security, would be a primary user of the database, according to the DHS filing. It's not immediately clear how the agency would use the technology to track immigrants, though DHS did say it expected the database to reduce the number of hours agents spend on surveillance.

Officials with ICE did not return a phone call Wednesday afternoon.

"There's no indication here that DHS has put in any privacy protections, so we don't know for what purposes agents could access this," Crump said. "How many people would access it? For what crimes? For less-serious crimes? What audit procedures would be in place?"

Private companies have already been capturing license-plate data through the use of scanners. Some advertise that they already have amassed one billion data points, according to Crump. Because they are private, there's not much known about how the data is used or brokered.

Pete Bigelow is an associate editor at AOL Autos. He can be reached via email at peter.bigelow@teamaol.com and followed on Twitter @PeterCBigelow.

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