A trusted service which publishes information describing security attributes of computing platforms in a defined physical area, for use by a visitor to a building, for example, who is unfamiliar with the computing platforms available for use therein. In a preferred embodiment, the system provides only details and/or a list of public keys of genuine trusted computing platforms within the area.In another embodiment of the invention, the information system comprises a trusted computing platform for providing selected information to a user's portable computing apparatus.