T-Mobile said an investigation into a data breach revealed that personal data, including social security numbers and driver's license information, of more than 40 million former and prospective customers was stolen.

The stolen files also included data from 7.8 million existing T-Mobile wireless customers.

Dates of birth, first and last names were also stolen, the telecom services provider said, adding there was no indication of their financial details being compromised.

The company, which had 104.8 million customers as of June, acknowledged the data breach on Sunday after US-based digital media outlet Vice first reported that a seller had posted on an underground forum offering for sale some private data, including social security numbers from a breach at T-Mobile servers.