In order to facilitate a user's ability to trust a computing environment, a trusted computing device (2) is arranged to challenge other devices in the computing environment and to record a log of the facilities available within the computing environment and an indication of whether those facilities are trustworthy. A new user (40) entering the computing environment can obtain the log from the trusted computing device in order to ascertain the status of the environment. Alternatively any device can hold data concerning platforms in its vicinity and its operation can be authenticated by the trusted device.