This paper discusses the concept of terrorism, who the terrorists are and develops an understanding of why they conduct the activities they do. Understanding the mens rea of the attacker will allow consideration of the type of attack they may plan and the effect they are likely to try and achieve. It looks at the main motivations of terrorist groups and discusses their use of the Internet for various aspects of a terrorist campaign such as propaganda and recruitment. It will consider the various tactics that have been used and how the Internet has provided a new opportunity for terrorists to conduct their campaigns and how it has been adapted by them for their purposes. It examines the potential threat of a cyber attack by terrorist organizations and how they can use the Internet and Cyber Space to attack a target with similar results to a conventional physical attack. The paper will briefly discuss some of the possible defences against this form of terrorism.