A computing platform 20 runs a compartmented operating system 22 and includes a trusted device 23 for forming an integrity metric which a user can interrogate to confirm integrity of the operating system. Also, the integrity of an individual compartment 24 is verified by examining status information for that compartment including, for example, the identity of any open network connections, the identity of any running processes, and the status of a section of file space allocated to that compartment 24. Hence, the integrity of an individual compartment 24 of the compartmented operating system 22 can be demonstrated.