TANs (Transaction Number) can only be used for personal transactions. Your bank will never ask you to enter a TAN for prize draws, security updates or to refund money to your account. Hence, please always use caution if you are asked for your bank details or a TAN when you are not actually making a transaction.
"You need to update your credentials", "Your account has been suspended", "You have won". What comes along is mostly a scam. You will be prompted to click a link and enter personal account information such as login name, TAN or PIN. Or you get a call or an SMS that want exactly the same thing: steal your data or your money directly. What to do in that case?