Since the first computer virus has been found, scanning detection has been used as a primarily method in virus detection systems. As computer viruses and worms become more complex and sophisticated, the scanning detection method is no longer able to detect various forms of viruses and worms effectively. Many anti-virus researchers proposed various detection methods including artificial immune system to cope with these characteristics of viruses and worms. This paper discusses some principle of artificial immune system and proposes artificial immune based virus detection system that can detect unknown viruses.