A hacker who stole the data of 54 million T-Mobile customers has called the carrier’s security “awful”.

John Binns, a 21-year-old American who now lives in Turkey, claimed responsibility for the hack on Thursday to the Wall Street Journal.

Binns claims he was able to gain access to the data of customers through a publicly exposed router.

"I was panicking because I had access to something big," he said. "Their security is awful."

Binns probed...