Modeling, simulation, and visualization play a significant role in the study of Information Assurance and Infrastructure Security. Research in this area is generally multidisciplinary in nature and collaboratively conducted by researchers with expertise in computer science, engineering, business, mathematics, and statistics. The paper presents modeling, simulation, and visualization of a hypothetical network system using the Easel agent-oriented programming language. The network system is represented as a multi-agent system. This multi-agent approach provides a more complete understanding of network attack and defense postures, network dynamics, and the computation of network security.