The U.S. Wireless carrier T-Mobile said Thursday that an unidentified malicious intruder breached its network in late November and stole data on 37 million customers, including addresses, phone numbers and dates of birth.

T-Mobile said in a filing with the U.S. Securities and Exchange Commission that the breach was discovered Jan. 5. It said the data exposed to theft - based on its investigation to date - didn't include passwords or PINs, bank account or credit card information, Social Security numbers or other government IDs .

"Our investigation is still ongoing, but the malicious activity appears to be fully contained at this time," T-Mobile said, adding that the data was first accessed on or around Nov. 25.

T-Mobile said it has notified law enforcement and federal agencies it didn't name.

The company has been hacked multiple times in recent years. In its filing, T-Mobile said it didn't expect the latest breach to have material impact on its operations.

But a senior analyst for Moody's Investors Service, Neil Mack, said in a statement that the breach raises questions about management's cyber governance and could alienate customers and attract scrutiny by the Federal Communications Commission and other regulators.

"While these cybersecurity breaches may not be systemic in nature, their frequency of occurrence at T-Mobile is an alarming outlier relative to telecom peers," Mack said.

In July, T-Mobile agreed to pay $350 million to customers who filed a class action lawsuit after the company disclosed in August 2021 that personal data including Social Security numbers and driver's license info had been stolen. Nearly 80 million U.S. residents were affected.