A computing entity comprises a trusted monitoring component having a first processing means and a first memory means, the trusted monitoring component being a self-contained autonomous data processing unit, and a computer platform having a main processing means and a main memory area, along with a plurality of associated physical and logical resources such as peripheral devices including printers, modems, application programs, operating systems and the like. The computer platform is capable of entering a plurality of different states of operation, each state of operation having a different level of security and trustworthiness. Selected ones of the states comprise trusted states in which a user can enter sensitive confidential information with a high degree of certainty that the computer platform has not been compromised by external influences such as viruses, hackers or hostile attacks. To enter a trusted state, references made automatically to the trusted component, and to exit a trusted state reference must be made to the trusted component. On exiting the trusted state, all references to the trusted state are deleted from the computer platform. On entering the trusted state, the state is entered in a reproducible and known manner, having a reproducible and known configuration which is confirmed by the trusted component.