In a statement on Experian’s website, CEO Craig Boundy (pictured) said no other clients but T-Mobile were affected. “It included access to a server that contained personal information for consumers who applied for T-Mobile USA postpaid services between September 1, 2013 and September 16, 2015,” he said.

The information accessed included names, dates of birth, addresses and social security numbers.

T-Mobile chief executive John Legere said: “Obviously I am incredibly angry about this data breach and we will institute a thorough review of our relationship with Experian. I take our customer and prospective customer privacy very seriously.

“This is no small issue for us. I do want to assure our customers that neither T-Mobile’s systems nor network were part of this intrusion and this did not involve any payment card numbers or bank account information.”