The ACLU in Virginia has launched what is believed to be the first legal challenge in the country against police for storing vast amounts of personal data obtained by scanning car license plates.

The Virginia branch of the civil liberties group is seeking to stop the police department in Fairfax County, just outside Washington DC, from storing the details of hundreds of thousands of vehicle license plates which it argues is an unacceptable invasion of privacy. The lawsuit says that the data, which includes the date, time and location of each vehicle scanned, is held for up to a year even though most of the individuals caught up in the data grab are suspected of no criminal activity.

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Concern about the practice of law enforcers indiscriminately scraping and storing data from vehicles using so-called license plate readers (LPRs) has grown steadily in recent months. Research by the ACLU nationally has shown that millions of Americans are now subject to such surveillance, the fear being that the information can be used to build up intrusive profiles on individuals and their behavior.

Earlier this year it was revealed that the Drug Enforcement Administration, in collaboration with another federal agency, had planned to use the automatic technology for surveillance of people attending public gun shows.

“Every time the government holds large amounts of personal information about individual people, there’s a potential for misuse. We’re very concerned about large databases being compiled that allow the movements to be tracked of ordinary Virginians,” said Rebecca Glenberg, legal director of the ACLU of Virginia.

Public records have shown that during the 2008 presidential election cycle, Virginia police used LPRs to monitor people attending rallies by Barack Obama and the Republican vice-presidential candidate Sarah Palin. They also tracked vehicles crossing the border between Virginia and Washington DC at the time of President Obama’s first inauguration.

Glenberg said: “In the abstract, license plate scanning may sound harmless, but many people would be alarmed to learn that law enforcement keeps whole lists of people engaging in specific political activities.”

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Fairfax County did not immediately respond to a request for comment from the Guardian.

License plate readers are usually attached to police patrol cars or on fixed posts, and are capable of recording thousands of plates per minute. The federal government has encouraged the proliferation of the technology with grants dolled out by the department of homeland security and other agencies.

The overt reason for collecting the data – to which the ACLU does not object – is to compare number plates against a “hot list” of stolen vehicles and criminal suspects, including sex offenders and fugitives. What civil liberties groups do object to is the passive use of the data and its long-term storage, even where no criminal activity is involved.

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In February 2013, the Virginia attorney general’s office released its legal opinion that data collected by LPRs should only be stored if it “specifically pertains to investigations and intelligence gathering relating to criminal activity”. On the back of that advice, the Virginia state police stopped using LPR technology and purged its databases of any information other than that prompted by active criminal investigations.

But individual police departments in counties across the state have continued passively to gather and store the data, prompting this week’s lawsuit which is seen as a test case in a relatively new area of the law. In the case of Fairfax County, the police department is party to a “memorandum of understanding” in which it shares all its license plate data with an unknown number of law enforcement agencies in the Washington DC area, thus compounding the privacy intrusions.

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