The development of the information and communication technologies with their extensive use from the governments and governmental organisations make them nowadays state vital components. This is also establishing critical infrastructures more vulnerable to advanced cyber threats, generated from terrorist groups and organisations. Terrorist use up-to-date tools and applications to perform cyber attacks, and usually are always step ahead from the personnel responsible for defending it. Terrorists usually use tools that can't be handled and analysed manually by an operator and require significant automation so that the cyber space can be effectively defended. The implementation of artificial intelligence (AI) based antivirus programs, showed that they are a useful tool for restricting cyber attacks, stop and react before or during the cyber attack. This chapter gives a brief review of techniques based on AI that already exists, emphasising the use of neural nets, expert systems and intelligent agents. Furthermore, it gives an overview of the AI based antivirus programs and their possible use in protecting of critical infrastructure and vital governmental infrastructure against terrorirst cyber attacks.