Increasing security for a hand-held data processing device with communication functionality where such a device includes an access-ordered memory cache relating to communications carried out by the device. The hand-held data processing device has a locked state that is entered by the device receiving or initiating a trigger. On occurrence of the trigger to enter the locked state the memory cache is reordered so as to disrupt the access-ordering of the cache to obscure device traffic information and thus increase the security of the device in the locked state.