Computing apparatus comprises a memory means storing the instructions of a secure process and an authentication process; a processing means arranged to control the operation of the computing apparatus including by executing the secure process and the authentication process; a user interface means arranged to receive user input and return to the user input; and an interface means for receiving a removable primary token and communication with the token. The token comprises a body supporting a token interface for communicating with the interface means, a token processor; and a token memory adapted to store token data including information for identifying the token and auxiliary token information identifying one or more authorized auxiliary tokens. The processing means is arranged to receive the identity information and the auxiliary token information from the primary token, to authenticate the toke using the authentication process and, if the token is successfully authenticated, permit a user to interact with the secure process via the user interface means. The processing means is arranged to repeatedly authenticate the primary toke and cause the computing platform to suspend interaction between the secure process and the user if authentication is not possible as a result of the removal of the primary token unless the primary token is replaced by an authorized auxiliary token.