![An AT&T store in New Jersey.](https://cdn.arstechnica.net/wp-content/uploads/2019/07/GettyImages-1017467916-800x640.jpg)
Enlarge / An AT&T store in New Jersey. (credit: Michael Brochstein/SOPA Images/LightRocket via Getty Images)
When Michael Terpin’s smartphone suddenly stopped working in June 2017, he knew it wasn’t a good sign. He called his cellular provider, AT&T, and learned that a hacker had gained control of his phone number.
The stakes were high because Terpin is a wealthy and prominent cryptocurrency investor. Terpin says the hackers gained control of his Skype account and tricked a client into sending a cryptocurrency payment to the hackers instead of to Terpin.
After the attack, Terpin asked AT&T to escalate the security protections on his phone number. According to Terpin, AT&T agreed to set up a six-digit passcode that must be entered before anyone could transfer Terpin’s phone number.