Because the networks and systems become more complex, the implementation of the security countermeasures for important Information Systems becomes more critical consideration. The designers and developers of the security policy should recognize the importance of building security countermeasures by using both technical and non-technical methods, such as personnel and operational facts. Security countermeasures may be made for formulating an effective overall security solution to address threats at all layers of the information infrastructure. But all these works can be done after assuming who is the threat agent. In this paper we identify the treat agents for information systems, summarize the characteristics of threat agents, and apply weighting factors to them.