https://techcrunch.com/2019/01/09/us-cell-carriers-still-selling-your-location-data/

Last year, four of the largest U.S. cell carriers were caught selling and sending real-time location data of their customers to shady companies that sold it on to big spenders, who would use the data to track anyone “within seconds” for whatever reason they wanted.

At first, a little-known company LocationSmart was obtaining (and leaking) real-time location data from AT&T, Verizon, T-Mobile and Sprint and selling access through another company, 3Cinteractive, to Securus, a prison technology company, which tracked phone owners without asking for their permission. This game of telephone with people’s private information was discovered, and the cell carriers, facing heavy rebuke from Sen. Ron Wyden, a privacy-minded lawmaker, buckled under the public pressure and said they’d stop selling and sharing customers’ locations.