A computer security system

摘要

A method of preventing unauthorised access to a host computer system (1) by a user at a remote terminal (2) is provided using paging system technology. In the method, a user inputs his user identification code input into the terminal (2) which transmits same to the host computer system (1). The system then generates a random code (Code A) and subjects Code A to a transformation characteristic of a transformation algorithm identified by the input user identification code so as to generate a transformed code (Code B). Code A is transmitted via a paging system (7), to a receiver (6) held by the user. The receiver (6) comprises transformation means adapted to transform the received Code A to a second transformed code (Code C), and means (9) for displaying Code C to the user. The user then inputs the displayed Code C to the terminal (2) which trasmits it to the host system (1). The input Code C is then compared with Code B and access is only permitted if Code C matches Code B.