• When the system asks the customer a question, it waits as long as necessary for the customer to answer. This could cause a severe security problem if the customer were to leave at this point without answering the question, since the ATM card would still be in the machine, generally with the customer's PIN having already been entered, thus allowing another user to "hijack" the session and perform operations like cash withdrawal from the customer's account.
While this seems unlikely, it is conceivalbe in some cases that a distracted customer might make this mistake. For example, after performing a transaction, the system asks the user "Would you like to do another transaction?". If the customer has just withdrawn cash, it is conceivable that the customer might place the cash in his/her wallet and accidentally forget about answering the the question and retrieving the card.
A real ATM typically has a timeout mechanism that begins beeping and ultimately ejects the card and ends the session if the user fails to respond within a certain amount of time. While a customer who leaves before this happens might inadvertently leave a card behind, at least the customer would not be "logged in" with his/her PIN. (Thus, the security risk is comparable to that resulting from a lost card, with the customer's account still PIN protected.) What changes would be needed to the system requirements, design, and code to improve security this way?