A firewall is one of the most common means to protect your PC against dangerous malware and other risks to your system. It is essentially a barrier between your PC and the Internet, a guardian or gatekeeper against invasive or malicious programs. A firewall is a system (or a network of systems) that can be thought of like a doorman operating a swinging door. The door swings one way and information is allowed in. It swings the other way and information is allowed out. A firewall is set by its owner or system administrator to obey certain rules regarding what is allowed to transmit in either direction. It is the doorman, both operating and guarding the system.



A firewall cannot make its own judgments about what should or should not be allowed to pass through it. That is up to the user. You need to do some research to find out what is going to work best for you but most commercially available firewalls come pre-configured in a way that works for most typical users. It can be installed either as hardware or software and can be customized based on your usage and your security needs.

A hardware firewall is a device that is installed between your computer and your internet connection point. For instance, if you have a cable modem, the firewall would plug into the cable modem and your computer would be plugged into the firewall. A software firewall is installed like any other program on your hard drive, either by CD or download. Software firewalls may also be built into your operating system, like Windows XP. You customize either one by using filters. Filters are the rules that the doorman in the earlier analogy uses to decide what is allowed in or out.

There are at least three basic methods that a firewall will use to control the transfer of information back and forth across its barrier. These methods may be used individually or in conjunction with one another. They are packet filtering, proxy service and stateful inspection.

Information travels on the Internet in little clumps of data called packets. A firewall using packet filtering stops the packets as they are coming into your system and examines them. It compares them against the filters you have set up, keeps what passes the test and discards anything that does not. A proxy service goes to get the data you request from the Internet and then brings it back to you safely. Stateful inspection is the new kid on the block. This method doesn't go through every part of a data packet like a packet filtering process does. Instead it compares certain elements of the packet to a database of information is has been told to trust. It compares the data you have been sending out to the data that is requesting to come in. If those two seem to match relatively well, it allows the exchange to occur. If the two don't line up well, the information asking to be allowed onto your PC is discarded.

All of these methods rely on the filters you have set up. These filters can be customized in many ways. You can block certain IP addresses to prevent a particular server from sending you information. An IP address is a numeric address assigned to every machine on-line. Each one is unique. If you find that one is problematic, you can block it. The numeric addresses are long and hard to remember and they may change so there are language-based names for servers on-line as well. They are called domain names and you can set your firewall to block certain ones. You can also filter out particular words or phrases to prevent a packet of data from entering your system. The words must be an exact match in most cases, however. So you may choose to block the phrase ?contains adult content? but a packet containing the phrase ?adult content? would slip by. You can also filter the protocol that your computer is allowed to receive. Protocol is how the machines talk to each other. There are protocols for video and audio exchanges, file transfers and text among others. When your firewall is working and some piece of information is rejected by your filters, most will alert you to the failure. It may ask you to give permission to allow the exchange of data to occur or allow the packet to be discarded or the program to be disabled.

Once your filters are set and your firewall is working, there is one thing from which it is completely unable to protect you ? yourself. If you are not careful to read and understand the alerts and not aware of what you are permitting to enter your PC, your filters will be rendered useless. You must make yourself a savvy user of the Internet. In addition, a firewall should not be your PC's only method of protection. Keep Windows updated by enabling the automatic update feature. Anitvirus software that includes current anti-adware and anti-malware components is an essential tool. Imagine our doorman again, only now he is accompanied in his task by a receptionist and a security guard.

Even when you know how firewalls work, the most important security feature your PC has is you.