I recently was shocked when using my banking app, you type the account number of another customer at the same bank (6 to 7 digits) and the app will fill out the name of the account owner (and ask you to check it is the person you want to send the money to), I really felt at unease by it and hope they limit this kind of lookup to a certain number of requests per user/day or someone could easily get access to all of the bank's customer names and their respective account number, this would be insanely dangerous.