A firewall is a technological barrier designed to prevent unauthorized or unwanted communications between computer networks or hosts. Most cable and DSL routers include a basic firewall. Also, a basic firewall is included in Microsoft Windows. Both of these solutions are better than nothing, but fall far short of really protecting you from spyware/malware infestations.
A high end firewall with content filtering will add features that allow you to increase the level of security and minimize the chances you will get malware and viruses on your network. A true firewall is actually a small computer that looks at every packet of information coming across the gateway between you and the outside Internet. It therefore can monitor and detect if the incoming data is malicious or if there is data coming from your computers that is suspect. The manufacturer of the content filtering hardware/software maintains a black list of nefarious website and charges you a small subscription fee to have your hardware updated with this list in real time. The firewall content filtering subscription will update its malicious website definitions and will not allow your computers to visit these sites. It will also allow you to block potential time wasters such as social networking and shopping websites.
It is our observation that many staff members waste untold hours each year on social networking, shopping and other personal web sites. Not only is this a waste of resources it puts your computers and data at risk. You will be able to block websites by category and specific sites. A nice firewall also lets you choose which computers are restricted.
There are many devices and services to firewall and content filter your network. There are standalone routers like Sonic Wall and Watch Guard. There are also open source software applications that can be run on an old/inexpensive computer with 2 network cards, such as Untangle. There are also services like Open DNS which can provide content filtering without a firewall. We use Sonic Walls for our clients because it is a more robust, reliable and easy to manage solution.