The personal information of about 15 million new T-Mobile customers was accessed on Thursday by hackers who breached into the mobile vendor's service provider that processes credit card applications.

In an announcement, the T-Mobile CEO John Legere confirmed that their Experian service experienced a "data breach."

"The investigation is ongoing, but what we know right now is that the hacker acquired the records of approximately 15 million people, including new applicants requiring a credit check for service or device financing from September 1, 2013 through September 16, 2015," Legere added.

He also disclosed that the information on the customers included their basic details like name, address and birthdate and also confidential information like their social security and identification numbers.

"Obviously I am incredibly angry about this data breach and we will institute a thorough review of our relationship with Experian, but right now my top concern and first focus is assisting any and all consumers affected. I take our customer and prospective customer privacy VERY seriously," the CEO furthered.

Legere noted that Experian has also assured them that steps have been taken to improve the protection of data.

According to TechCrunch, the global information services group also notified customers affected of the breach then secured their servers.

"It also is offering consumers two years of identity resolution services," added the same report noting that it is still unclear who was responsible for the hack.

Both companies have also reportedly warned their customers not to provide personal information to anyone who would be asking for it through phone calls or message but noted that they can still visit the companies' websites.

Though, this will not result to closing of bank or credit card accounts, TechCrunch said the customers "are at an increased risk of identity theft."

The stolen data, as per CNN, could be sold in black markets. "Hackers then amass the stolen information to build large, searchable databases that make it easy for anyone to steal your identity for a small price. A stolen identity leads to stolen tax refunds, ruined credit and worse," explained the same report.

This is the first major hack in the US as SkyNews said that other well-known companies have also been victimized like Sony Pictures, Home Depot and eBay.

Now, the hackers have targeted third biggest mobile network in the country, focusing primarily on the credit card profiles of their customers.

There is surely fear for compromised customers which the two companies still need to address with a better assurance that they will not fall victims to identity thieves and that the same incident will not happen again.