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.
After you have logged into online banking for the first time, you will be asked to change your PIN. Please make sure to make your PIN as secure as possible.
That means staying away from using obvious character combinations such as your first name and birth date. Try using a word that is meaningful to you or easy to remember phrases and their acronyms.
Also, always use a character combination that you are not using anywhere else.