The Department of Homeland Security (DHS) used mobile location data to track people’s movements on a much larger scale than previously known, according to new documents unearthed by the American Civil Liberties Union (ACLU).

It’s no secret that U.S. government agencies have been obtaining and using location data collected by Americans’ smartphones. In early 2020, a Wall Street Journal report revealed that both Immigration and Customs Enforcement (ICE) and Customs and Border Protection (CBP) bought access to millions of smartphone users’ location data to track undocumented immigrants and suspected tax dodgers.

However, new documents obtained by the ACLU through an ongoing Freedom of Information Act (FOIA) lawsuit now reveal the extent of this warrantless data collection. The 6,000-plus records reviewed by the civil rights organization contained approximately 336,000 location points across North America obtained from people’s phones. They also reveal that in just three days in 2018, CBP obtained records containing around 113,654 location points in the southwestern United States — more than 26 location points per minute.

The bulk of the data that CBP obtained came from its contract with Venntel, a location data broker that aggregates and sells information quietly siphoned from smartphone apps. By purchasing this data from data brokers, officials are sidestepping the legal process government officials would typically need to go through in order to access cell phone data.

Documents also detail the government agencies’ efforts to rationalize their actions. For example, cell phone location data is characterized as containing no personally identifying information (PII) in the records obtained by ACLU, despite enabling officials to track specific individuals or everyone in a particular area. Similarly, the records also claim that this data is “100 percent opt-in” and that cell phone users “voluntarily” share the location information. But many don’t realize that apps installed on their phones are collecting GPS information, let alone share that data with the government.

The ACLU says these documents are further proof that Congress needs to pass the bipartisan Fourth Amendment Is Not For Sale Act, proposed by by Senators Ron Wyden (D-OR) and Rand Paul (R-KY), which would require the government to secure a court order before obtaining Americans’ data, such as location information from our smartphones, from data brokers.

Shreya Tewari, the Brennan Fellow for ACLU’s Speech, Privacy, and Technology Project, said: “Legislation like the Fourth Amendment Is Not For Sale Act would end agencies’ warrantless access to this data and head off their flimsy justifications for obtaining it without judicial oversight in the first place.”

Spokespeople for Venntel and Homeland Security did not immediately comment on the report.

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