Hackers got away with the personal information of 15 million T-Mobile customers by breaching the company that processes its credit checks.

That firm, Experian, said Thursday that a breach grabbed T-Mobile customer data from September 1 to September 16.

Stolen data includes names, birth dates, addresses, social security and drivers’ license numbers, but not credit card or payment information, according to the company. Still the stolen data could lead to identity theft.

Experian CEO Craig Boundy said in an online post that the hack did not affect its credit bureau business or its consumer credit database.

T-Mobile CEO John Legere commented in tweets a blog post and a FAQ page, saying he’s “Incredibly angry about the data breach and we will institute a thorough review of our relationship with Experian.”

Experian said it is notifying affected customers. It also warned them to be careful about emails and other attempts to profit from the stolen data.

You have to wonder why the large number of recent security breaches have not led every firm handling personal customer data to review and harden their systems. But apparently, they have not.

Here’s Experian’s response from its CEO Craig Boundy: http://www.experian.com/securityupdate/

For more information regarding the investigation and the actions Experian is taking to protect consumer information, please visit www.experian.com/T-MobileFacts.