T-Mobile suffered a security breach in December that may have exposed call-related information and phone numbers for some of its customers. The information affected did not include names on customers’ accounts, physical or email addresses, financial data, credit card information, social security numbers, passwords, or pins.

T-Mobile said in a statement that it notified’less than 0.2 percent’ of its customers that some account information may have been illegally accessed. Affected customers were notified via text message.

T-Mobile said its security team’shut down malicious, unauthorized access’. It began an investigation to determine what information was involved. T-Mobile reported the situation to federal law enforcement.