Comparable to a physical firewall that keeps fire from spreading from one area to another, a computer firewall is a blockade in the form of a program or hardware device designed to keep unwanted information from coming through your Internet connection.
Seeing how firewalls are customizable, you can add or remove filters based on several conditions. The most common of them being IP addresses domain names, protocols, ports and specific words and phrases.
Using one or more of the three currently available methods, firewalls control traffic moving in and out of your network.
Packet filtering
Packets (small amounts of data) are interpreted against a set of filters. Data that successfully moves through the filters are sent to the requesting system. Any data unsuccessful is discarded.
Proxy service
Retrieved by the Internet, this information is sent to the requesting system and vice versa.
Stateful inspection
The newest method that does not look at the contents of each individual packet, but instead compares key parts against a database of trusted information. If the contents are deemed reasonable, it is allowed through the firewall, otherwise it is discarded.
With the internet brimming with an overwhelming amount of creative ways for deceitful people to worm their way into your system, a firewall should be a necessary part of your business.