Around 15 million US T-Mobile users have had their personal information stolen in a data breach at credit agency Experian.
The company, used by T-Mobile to check the background of customers, saw stolen names, date of births and social security numbers – stopping short of acquiring actual payment details.
T-Mobile chief executive John Legere said: “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.
"Experian has assured us that they have taken aggressive steps to improve the protection of their system and of our data."
On the receiving end of the criticism, an Experian statement claimed that the breach was discovered 15 September 2015 and was immediately reported to the police.
Experian is informing those affected by email, offering them free credit monitoring and identity resolution services for two years.