“Computer firewall” is software which is developed on the basis of operating system. It was mainly designed for control the access to unauthorized content on a computer. It works under some rules and instructions. According to those rules it decides whether to block or allow access.

Computer firewall is the firewall software used by many users who are working on Microsoft windows. They can easily access this firewall program. This firewall acts quickly to prevent Trojans and blocks the access of the network. This blocking technique is possible when the application criteria changed.

This firewall technology was found in the 1980s, when internet itself had not reached the people widely. Routers were used to separate network accessibility and the demand for network security was not necessary.

Day by day the use of internet access is gradually increasing. It leads to develop more applications for internet security. By this firewall was lunched for security administration. Windows firewall is available with the purchase of windows OS.

Firewall functions under certain set of rules and instructions. If it is not working it will become worthless. Optimized analysis makes changes in settings of security administration. All these are working for complete protection.

Adding of new features and new applications firewall software classified into three generation sets. All these firewall generation software supports both online and offline services. By this user can protect their computers. Firewall software controls the installation of new programs, copying g and sharing of data.

The first developed filter system which is known as “packet filter”. It is first generation firewall which was worked on data transfer from the networks. The second generation firewall which is known as “stateful filter”, this firewall maintains records of all connections passing through the firewall.

The third function is a proxy based application layer firewall. This detects the applications and protocols sneaking in, through the non standard ports. Harmful and abused protocols are also blocked.

Application layer-firewalls works on the application level of the TCP/IP stack and may intercept all packets traveling to or from an application. They block other packets. These application firewalls will prevent all unwanted outside traffic from reaching protected machines. On inspecting all packets for improper content, firewalls can prevent outright the spread of networked worms and most harmful Trojans.