T-Mobile is blaming a “bad actor” for a data breach affecting approximately 37 million customers.

The company said the breach started around Nov. 25. Once they recognized the problem, T-Mobile said their team shut it down within 24 hours.

The breach compromised customers’ names, addresses, email, phone numbers, dates of birth and some information about their plans, according to T-Mobile. The company says sensitive information like social security numbers and financial account information was not compromised.

The cell phone carrier says it has notified law enforcement agencies and federal agencies about the breach.

In addition, it says it is in the process of informing all impacted customers.