According to a news by Reuters, data belonging to 40 million customers of T-Mobile was stolen in a recent data breach. This news made it to the security sites in last few days but T-Mobile had not confirmed it yet. Finally, T-Mobile has announced after proper verification that there was really a data breach and the data of 40 million customers was stolen. This is different from the claim made by the hackers who said that the data belonged to 100 million customers.
The stolen data includes IMEI number, IMSI number, mobile phone number, drivers license, social security number, first name, last name, and the date of birth. The data may or may not include all of this information for all the customers. For example, according to KresbOnSecurity, for the prepaid customers only IMEI and IMSI numbers were available in the data. This data includes both the former customers and the current customers.
So how do you check whether your information was also leaked if you are or have ever been a T-Mobile customer? Sites like Have I been Pwned? make it very easy to check. Sooner or later the data breach will be included in their database. So all you have to do is visit https://haveibeenpwned.com/ and click on the Notify Me button. You have to enter your information and it will inform you whenever your information appears in any of the data breaches.
You can also check their website from time to time by entering your mobile number or email address. If your mobile number appears in any of the known data breaches, then it will alert you instantly. In addition, we can expect T-Mobile to inform the affected users in near future about their data leak. They will also (they should) inform publicly about which steps the customers should take to stay safe after such a data breach.