A system comprising a trusted computing platform including one or more logically protected computing environments, each of which is associated with at least one service or process supported by said system, the system being arranged to load onto said trusted computing platform a predetermined security policy including one or more security rules for controlling the operation of each of said logically protected computing environments, the security rules for at least one of said logically protected computing environments including an execution control rule which defines the security attributes to be applied to a service or process associated with said logically protected computing environment when said service or process is started.