Abstract: A simple, convenient and reliable method provided for identifying a user through a computer network. This method comprises the steps of sending a string of characters randomly selected from a table recording a set of characters from a central computer to a terminal computer, converting one or more characters from the string according to a conversion rule, sending one or more characters from the terminal computer to the central computer and identifying the user of the terminal computer based on the string of characters sent from the central computer, the conversion rule and the one or more characters sent by the user.