In a building, a structural firewall prevents damage from propagating across the entire building. It holds potential danger at bay and limits exposure. In a computer the firewall prevents data from going where it should not go.

In a simple application, the firewall prevents information that was not requested from coming into your computer. If you type the address for, for example, data from their web servers can come to your computer because you initiated the communication. On the other hand if a malicious website wants to initiate the transfer of data from their website to your computer without your request, your firewall can be programmed to prevent this action based on the fact that you did not first initiate a connection to the website.

A building security system is very effective in helping to manage and monitor security within a building. Computer traffic, since it does not pass through doors and is not monitored by motion sensors, is not protected by the business security system. A network firewall is akin to the building security system. The network firewall though focuses on the wired and wireless network traffic coming into the building, leaving the building, and sometimes even within the building itself.

Firewalls, if configured properly, can perform many specific tasks to protect the network and computers.