Investigators raised alarm bells when they learned Homeland Security bureaus were buying phone location data to effectively bypass the Fourth Amendment requirement for a search warrant, and now it’s clearer just how extensive those purchases were. TechCrunch notes the American Civil Liberties Union has obtained records linking Customs and Border Protection, Immigration and Customs Enforcement and other DHS divisions to purchases of roughly 336,000 phone location points from the data broker Venntel. The info represents just a “small subset” of raw data from the southwestern US, and includes a burst of 113,654 points collected over just three days in 2018.

The dataset, delivered through a Freedom of Information Act request, also outlines the agencies’ attempts to justify the bulk data purchases. Officials maintained that users voluntarily offered the data, and that it included no personally identifying information. As TechCrunch explains, though, that’s not necessarily accurate. Phone owners aren’t necessarily aware they opted in to location sharing, and likely didn’t realize the government was buying that data. Moreover, the data was still tied to specific devices — it wouldn’t have been difficult for agents to link positions to individuals.

Some Homeland Security workers expressed internal concerns about the location data. One senior director warned that the Office of Science and Technology bought Venntel info without getting a necessaryPrivacy Threshold Assessment. At one point, the department even halted all projects using Venntel data after learning that key legal and privacy questions had gone unanswered.

More details could be forthcoming, as Homeland Security is still expected to provide more documents in response to the FOIA request. We’ve asked Homeland Security and Venntel for comment. However, the ACLU report might fuel legislative efforts to ban these kinds of data purchases, including the Senate’s bipartisan Fourth Amendment is Not For Sale Act as well as the more recently introduced Health and Location Data Protection Act.

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