An anonymous reader writes: A bug in T-Mobile's website let anyone access the personal Account Details of any customer with just their cell phone number, ZDNet reported Thursday. The flaw, since fixed, could have been exploited by anyone who knew where to look -- a little-known T-Mobile subdomain that staff use as a customer care portal to access the company's internal tools. The subdomain -- promotool.t-mobile.com, which can be easily found on search engines -- contained a hidden API that would return T-Mobile customer data simply by adding the customer's cell phone number to the end of the web address. Although the API is understood to be used by T-Mobile staff to look up account details, it wasn't protected with a password and could be easily used by anyone. The returned data included a customer's full name, postal address, billing account number, and in some cases information about tax identification numbers. The data also included customers' account information, such as if a bill is past-due or if the customer had their service suspended.

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