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.
An up-to-date anti-virus program and personal firewall is essential for protecting your computer from harm. All conventional operating systems already come with a firewall that will monitor incoming and outgoing connections.
It is important to regularly update your anti-virus program to make sure it is capable of protecting you from the latest virus' and Trojans. It is also important to regularly scan your entire computer for viruses.
All of the above also applies to smartphones. However, different smartphones might require different security methods. For more information, please contact the relevant manufacturer.