The Federal Communications Commission (FCC) launched an investigation into T-Mobile after the telecommunications giant disclosed it suffered yet another significant cybersecurity lapse exposing customer information.

T-Mobile said in a filing with the Securities and Exchange Commission on Thursday that a bad actor used a single application programming interface to obtain the data of approximately 37 million current postpaid and prepaid customer accounts. The company said it found no evidence the bad actor breached or compromised its systems and that it shut the issue down within 24 hours of identifying it on Jan. 5.

Affected information included names, billing addresses, email addresses, phone numbers, dates of birth, and T-Mobile account numbers and features. No passwords or financial information were exposed, according to the company.