National security poses the most difficult of practical problems in respect of information. ‘Information Warfare’ has become an important aspect of the agencies that defend national security. National security concerns what many regard as the quintessential function of the state. It involves the most developed form of information technology – most highly secret and according to renegade security agent David Shayler much of the intelligence is unreliable, an accusation that was vigorously denied. The allegation resurfaced in relation to the use of intelligence to justify the war in Iraq. The subject covers the most intrusive of information-gathering exercises conducted on behalf of government agencies. National security is also a virtually unanswerable plea to immunity and confidentiality, preventing access by individuals to information upon themselves. As we shall see in chapter 11, the courts have long shown themselves sensitive to executive assertions of national security precluding judicial investigation of an individual grievance. Although there are indications of increasing unease where the plea is put to a strained use, the courts have nonetheless reminded themselves of their limited role when assessing questions concerning executive judgements involving national security. Many of the most controversial cases concerning information in recent years have related to national security. The peculiar potency of the subject must be fully realised. It is not characteristic of all areas of government activity. However, it will provide an interesting area of human activity in which some of the theoretical points in chapter 1 above may be tested.