A computer system should provide confidentiality, integrity and assurance against denial of service. However, due to increased connectivity (especially Internet), and the vast spectrum of financial possibilities that are opening up, more and more systems are subject to attack by intruders. When the computer came into existence the minimum security provided is the user name and password protection. Through which it is easily detected and misuse can happen very often. Later when the encryption came into existence with various encryption techniques/algorithm, the intruder can able to trace out the encrypted code. Next level of improvement is in the form of network security.