The new information and communication technologies bring many benefits to society, but they also create new social and ethical problems — such as software theft, invasions of privacy, hacking and the creation of viruses. Computer-assisted crime is one of the most serious and its apparent growth in recent years demonstrates clearly how new technologies create new opportunities for criminal activity. The available evidence on the nature and extent of computer crime is reviewed, together with the available data on participation. Techniques for improving computer security are then discussed and the appropriate lessons drawn.