If you are a regular internet user, be it at home or at work, chances are you have heard the term a"firewall". When asked what exactly a firewall is though, many people have a limited amount of knowledge, knowing only that it is something that protects computer systems.

Quite simply, this is correct; the basic principle behind a firewall is to act s a barrier between the internet and a local computer. This local computer can either be a standalone system, part of a home network or a larger office network.

Regardless, a firewall works the same way by keeping out unwanted hackers and/or preventing users from performing certain actions (e.g. viewing offensive websites or downloading programmes).

A firewall can either be located on a computer system, (known as a software firewall), within a network router, (known as a hardware firewall), or both.

Nearly all of today's network routers have built in firewalls which can be configured via the computers internet browser to which they are connected. Most home computer systems are pre-installed with a software firewall; there is also a great deal of free firewalls available on the internet.

Both hardware and software firewalls work in similar ways to keep your system secure and for maximum security a combination of the two is recommended. In order to protect your system a firewall uses one or both of the following methods:

* Packet Filtering is used to compare data (or packets) that reach the firewall to predefined filters, if the data complies with the filters then it is allowed through, otherwise it is dropped.
* Stateful inspection is a newer technology which unlike packet filtering does not analyse the whole packet, but just key parts. Specific characteristics of outbound packets are compared to inbound packets and if the comparison is acceptable the data is allowed into the network, otherwise it is dropped.

By using the above technologies users are able to allow or deny traffic into and out of their network based upon IP addresses, domain names, protocols and ports.