The diagram to left shows an unprotected system using a DSL modem. As you can see, someone on internet can attach computer system easily as DSL modem provides no protection (some DSL modems have built-in firewalls). An attacker can get through any type of modem - DSL, cable, 56K, 28.8 or whatever. If device gets you on internet, you are vulnerable.

For those with a DSL, cable modem or other "always-on" connection, you MUST get a firewall. This is critical, as your machine is always live and it most likely has a fixed IP address. This makes it easier for your system to be "found" and attacked.

What a personal firewall does is isolate your computer from rest of internet. It does this by inspecting each packet of data to determine if it it should be allowed to get to (and in some cases from your machine.) The best protection completely hides your computer - this is called stealth mode.

You have option of installing a software firewall or a hardware firewall.

Software Firewall - A software firewall runs on your computer system in background. It intercepts each network request and determines if request is valid or not. Software firewalls offer following advantages:

- They are generally very inexpensive

- They are very easy to configure

They have following disadvantages:

- Since they run on your computer they require resources (CPU, memory and disk space) from your system.

- They can introduce incompatibilities into your operating system.

- You must install exactly correct version for your operating system.

- You must purchase one copy for each system on your home network.

Hardware Firewall - A hardware firewall is generally a small box which sits between your computer and your modem. In general, hardware firewalls have following advantages:

- They tend to provide more complete protection than software firewalls

- A hardware firewall can protect more than one system at a time

- They do not effect system performance since they do not run on your system.

- They are independent of your operating system and applications.

They have following disadvantages:

Most people don't have anywhere near that number, but I'll bet you have at least a couple of dozen. Let's see, you've probably got an account at your bank's website, a few credit cards, egroups, perhaps a few webrings, your ISP, email, hotmail, perhaps AOL, and a few others that you don't use as often.

If you are like most people, you cannot even come close to remembering it all. In fact, a lot of people simply create same account name and password everywhere ... and that's extremely dangerous.

Let's say a hacker figures out your AOL account and password. If every other account that you own has same username and password ... well, you get idea. Now all he has to do is figure out where you have accounts ... but he could just try it at a number of say, banking sites or credit card sites, and perhaps he will get lucky. You may make it even easier for him by mentioning your sites in your AOL emails or on your web site.

So how do you protect yourself? First, make sure your passwords are all different. Don't use same password on all of your accounts ... and try and use a few different usernames if you can.

Next, be sure and choose some password that are not so easy to guess. Avoid names (husband, wife, kids, cats and so on), social security and phone numbers, addresses and anything else that someone could figure out if they knew anything about you.

Also avoid some common words. Did you know that most common password is simply "password". "God" is also common, especially amoung system managers. Avoid common words such as these.