This paper discusses prevention and protection of computer and information systems against the criminal offense of computer crime. Computer crime does not have a generally accepted definition and in order to describe and define it more accurately, it is necessary to pay close attention to the ways, means and consequences of execution of acts that can be performed by chance, for social or political purposes, as well as for study, planning and engagement of professional criminals. It is closely related to computer technology and the internet, which also includes marketing information systems, whose goal is to provide information needed to make decisions related to marketing. As in defining of the concept of computer crime itself, as well as in the defining of forms, there are no generally accepted criteria or a unique methodology, which is caused by the continuous development and application of new technology. As computers become an almost indispensable part of human life and work, the danger of computer crime is growing, and thus prevention and protection against computer crime is becoming increasingly more necessary and important. System security can be endangered by people, things and events which come from the inside of the system itself or from its environment, and some of their actions can be expected and predicted, but some can’t. In order to prevent and protect against computer crime, various methods and means of protection are required to ensure the smooth and secure operation of system, data and communication within the system and towards the environment. The above-mentioned methods and means are in fact technological protection, and in addition to them effective legal protection is needed as well, especially criminal law protection whose purpose is preventive action directed at the non-perpetration of the offense of computer crime. Besides technological and legal protection, ethical, educational, governmental and organisational activities as well as IT and telecommunications technology play an important role in the prevention of computer crime. Fighting against computer crime is a task for the entire society and its effectiveness depends mostly on the assumptions of effective prevention.