The world is becoming more interconnected with the advent of the Internet and new networking technology. Over the past few years, Internet-enabled business, or e-business, has drastically improved efficiency and revenue growth. However, as networks enable more and more applications and are available to more and more users, they become ever more vulnerable to a wider range of security threats. Therefore, to combat those threats and ensure that network transactions are not compromised, network security has become more important not only for business and the military, bur also for organizations and personal computer users.
In the past, hackers were highly skilled programmers who understood the details of computer communications and how to exploit vulnerabilities. Today almost anyone can become a hacker by downloading tools from the Internet. These complicated attack tools and generally open networks have generated an increased need for network security and dynamic security policies. Many organizations try to classify vulnerability and their consequence: one the most famous vulnerability database is National Vulnerability Database from MITRE corporation [1].
The entire field of network security is vast and in an evolutionary stage; security incidents are rising at an alarming rate every year. Despite significant advances in the state of the art of network and computer security in recent years, systems more vulnerable than ever. Each major technological advance in computing raises new security threats that require new security solutions, and technology moves faster than the rate at which such solutions can be developed. As the complexity of the threats increases, so do the security measures required to protect networks.