A method and apparatus provide security for a network-connected vehicle (or other networked environment) in which a predefined set of permitted operations relating to protected resources can be initiated remotely from elsewhere in the network, while security is maintained for the protected resources (for example, an engine performance optimisation control unit or air conditioning control unit within a vehicle) by preventing remote initiation of any other operations on a data processing unit which is connected to the protected resources. One of a pair of gateway components runs on each of two data processing units within the vehicle (or other environment), the first processing unit being connected to the vehicle's device control units and the second processing unit being connected to the external network. The gateway components control the types of communications which can be passed from the network-connected side to the first processing unit such that only permitted operations can be requested and no unauthorised operations can be initiated remotely.