Abstract:- This paper present a review of how to secure our computer network. Today's attacks are succeeding far too frequently, all due to the limitations of legacy security tools. Because many security technologies arose in an earlier era—when attacks targeting sensitive information were fairly straightforward to identify—these tools fail when they cannot recognize a previously unknown attack or threat vector. In the last few years, the scale and sophistication of IT security threats have grown at an explosive rate. Organizations have to contend with industrialized attacks, which, in some cases, rival the size and sophistication of the largest legitimate computing efforts. In addition, they also have to guard against a more focused adversary with the resources and capabilities to target highly sensitive information, often through long-term attack campaigns.