Firewalls are not exactly walls of fire in cyberspace. It is basically named as such because it is an impassable boundary to most Internet traffic. It forms a wall around networks or individual computers protecting them from potential harm. Harm in this sense refers to hackers and malware programmers or misdemeanors such as ping flood attacks. Firewalls are not completely foolproof as they have to be configured to allow some traffic in and block all other traffic out.
This fallibility (by making humans do most of the judgment) is very dangerous as in the hands of an inexperienced user, will expose the network or particular computer to harmful traffic even if it is in place. There are ways to work around a firewall, even if an experienced user configures it. Thus, as with all methods this technique is not without its weaknesses. However, for everyday, mainstream users, most firewalls out there do a very good and effective job in protecting them.
Software firewalls are basically programs that filter all Internet traffic through them. There is a wide variety of software firewalls out there, with many of them being freeware or shareware. Software firewalls are more suitable for the average user as they can be easily configured and can be easily shut down if by any chance they cause problems. However, this ease and convenience of course comes with its price.
Firstly, users may unwittingly block legitimate traffic from ever entering their computers. As a result, they get frustrated by the fact that they can do very few things successfully on the Internet. Also, the fact that they can be easily shut down also means a hacker can easily send a Trojan Horse over to quietly shut down a user’s firewall which was running in the background. When this happens, a hacker will get complete access to the user’s system. Software firewalls also consume a lot of processing power, especially if the computer’s CPU is not built for speed. Software firewalls are thus, unsuitable for corporate users who have much more at stake.
Hardware firewalls are more suited to corporate users. These are usually embedded as a chip in network routers and can be controlled by a system administrator. The best part about hardware firewalls is that most average users do not know how to meddle with it, thus it will ensure that only people who know what they are doing can set this firewall for a higher level of security. Hardware firewalls also do not consume memory or processing power from the computer it is protecting. They cannot be shut down programmatically or remotely, making them a much safer choice.
Firewalls are like castle walls protecting the wealth within from those who seek it. They cannot be overcome easily but are not invincible.
Reference
Home PC Firewall Guide
http://www.firewallguide.com
How Firewalls Work
http://www.howstuffworks.com/firewall.htm
Internet Firewalls: Frequently Asked Questions
http://www.interhack.net/pubs/fwfaq/