Disclosed is a method of providing network security within a mobile radio communications network and including creating a security context for communications between a mobile radio communications device and the network, the security context being created responsive to an input parameter such as the downlink NAS count, and the method further including, as part of each initial handover attempt, controlling the parameter so as to apply a version of the parameter different from a previous version, for example as incremented downlink NAS count, and preferably independently of network signaling messages.