Here is the most updated info from T-Mobile
It turns out 47.8 million customers were affected (which is about 1/2 their US customer base). It breaks down to 8 million cellular accounts and 40 million prospective customers that applied for credit. Keep in mind credit was pulled in the past whenever new customers signed up or financed a phone. (T-Mobile and Sprint now are one company. I don’t know how many of these records pertain to old Sprint customers or if they are pre-merger T-Mobile accounts). T-Mobile CLAIMS that no financial data, like Social Security #’s were accessed.
Here is what they are doing however. They are going to offer two years of ID theft protection through McAfee. I’m going to skip that. McAfee hasn’t done anything good for computer security since the 1990s. The late, great company founder John McAfee despised what his old company had become before his death. You can sign up for it if you wish, but I would prefer that you obtain all of your credit reports from annualcreditreport.com, then sign up for a credit freezes or at the very least fraud alerts.
Secondly — here is something you can take action on today. T-Mobile is asking you to change your account PIN. This is also known as a billing passcode. You can do it online or you can call 611 from your phone and talk to customer service. If that billing passcode is in the wrong hands — someone can port your number out — steal it and take it to a different company.