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.
Specify a daily limit for your online banking transactions. Doing so will limit the maximum amount of money that can be withdrawn from your account each day using online banking. This is a very easy and practical method to limit the amount of money available each day in a way that suits your needs, and to limit the risk of unauthorised access.