Many people have it installed on their computer, but only a few of them know what a firewall actually is and how it works. The expression "firewall" is in itself relatively meaningless, especially when considering that it is one of the most important components in every computer network, and especially on the internet. What is striking is that the expression "firewall" does not even slightly indicate what kind of machine or program in a computer network one is referring to.

The firewall actually is, as already mentioned, a computer network security component. It usually serves as a kind of gatekeeper between two networks and regulates the traffic between these networks. It basically says which data packages are allowed to pass the network borders and which one's are not. There are several types of firewalls. The bigger one is the hardware firewall, which is a physical network component that is usually connected between two or more network plugs. In contrast to the dedicated firewall, there is the so-called software firewall. It is basically a program that is installed on a normal PC, and that acts like a hardware firewall by blocking the internet connection for all unknown programs. As this kind of firewall can only protect a single PC, it is often also called personal firewall.

Setting up a personal firewall is relatively easy. One has to install a program, and that's it. Setting up a hardware firewall for a big computer network, for example a company-wide network, is a very complex matter. It should in principle be done by somebody who has detailed knowledge about the technology.