It later turned out John Edens didn't have a warrant, nor was he from law enforcement at all. Instead, he was a debt collector with a history of stalking and domestic violence who had managed to get ahold of Johnson's phone location data. He did this by pretending to be a U.S. Marshal with the "Georgia Fugitive Task Force" to T-Mobile, which then provided Edens with the location of Johnson's phone in a handy Google Maps interface—"pinging" the phone, in industry parlance.

Ruth Johnson didn't know exactly who rang her phone and threatened her around 20 times in 2014. The person on the other end said he was John Edens from the U.S. Marshals with a warrant for her arrest for stealing a car. She was behind on her payments.

"Fearful," is the word Johnson first used to explain the episode in a phone call with Motherboard. "It was very fearful."

Motherboard previously reported on Edens' case using court documents and sources in the bounty hunting industry; Edens was sentenced to one year in prison for impersonating a U.S. officer. Now, Johnson explained in an interview what it was like to have her phone tracked. Her story demonstrates the very real human impact that the black market use and sale of phone location data can have.

"I was very upset with the phone company, because I was under the impression that you had to get [a] court order in order to get information such as that out," she said. T-Mobile "put my life in danger," she added.

The harassment was relentless. Edens turned up at Johnson's place of work. Someone banged on her home's door at 3 a.m., then Edens turned up on her porch another day. Johnson said her husband had been recently killed and Johnson didn't know if this harasser was somehow connected to his murder, compounding her fear. Her teenage daughter moved 10 hours away to be with her grandmother, just to feel safe.

"You cost me my family," Johnson said, referring to T-Mobile.

Do you work in the location data industry? Did you used to? We'd love to hear from you. Using a non-work phone or computer, you can contact Joseph Cox securely on Signal on +44 20 8133 5190, Wickr on josephcox, OTR chat on jfcox@jabber.ccc.de, or email joseph.cox@vice.com.

In a panicked rush, Johnson ended up moving to a different neighborhood altogether, she added. She gave the car back to the dealership she owed payments to, wanting to avoid any more trouble.