Experian, the credit monitoring company used by T-Mobile to check the credit history of potential customers, recently experienced a data breach that has left a fourth of the company’s customers vulnerable.

T-Mobile is the third largest mobile service carrier in the United States and an industry heavyweight abroad.

The hacker obtained access to the sensitive information of about 15 million T-Mobile customers, including Social Security numbers, drivers’ license numbers, and passport numbers. Those who participated in a credit check from T-Mobile between Sept. 1, 2013 and Sept. 16, 2015 are particularly at risk.

The vulnerable point—the credit check service—can be quite useful. If you’re using T-Mobile for communication with international offices and travel out of the country, you may want to consider taking advantage of the credit monitoring services provided for free to T-Mobile customers. Even if you don’t fit the criteria for the information stolen during the breach, you can take advantage of the monitoring service—T-Mobile has extended it to all customers.

The catch: Experian, the company who lost the data in the first place, provides the service. Take your chances or take this opportunity to monitor your credit elsewhere.

By Prasana William