Unless you have a very old computer, it probably has a "firewall" built into it. That may be the Windows firewall provided with XP, or a firewall included with your antivirus software.

What is it for? It's to help keep bad things out of your computer and also (with some firewalls) to keep your computer from doing bad things to someone else.

But wait, you say: I thought that was what virus software does? Well, yes, but it's a little different. Virus software examines things you bring into your computer (web pages, email) and tries to make sure they are safe. It's like a parent checking the bag of Halloween candy their child brought home. A firewall is a lock on the door: it stops things you don't want coming in at all.

Take a very simple case: your printer. You want to be able to print to it, of course, but you don't want me to be able to use it from here, right? A firewall is part of what protects you from that - and of course much worse. If, for example, you just "hook up" to the internet without any protection at all, your computer will be "owned" within hours - sometimes minutes. That is, someone will have hacked into it, taken control, and will probably use it as part of a vast network of such hijacked computers that are used for sending spam emails and other criminal purposes. That's not a joke, not an exaggeration: it's real. You won't even know that your computer is doing this, though it may run more slowly and "act up" more.

So a firewall is a good thing. But - particularly with the third party firewalls like those that come with Norton AntiVirus, McAfee and others, a firewall can also be the source of computer problems, glitches, and mysterious behavior. When I am working at customers sites, I often find that misbehaving firewalls are the source of the problem I was called to fix.

If something is odd, if your computer is suddenly acting strangely, the first thing to try is turning off the firewall if you have one. How you do that varies, but third party firewalls often show up in your System Tray; if you right click on them, a menu usually comes up that will let you temporarily or permanently disable them. Windows Firewall can be disabled in Control Panel. Often shutting off these firewalls fixes your problem instantly.

Didn't I say that you need a firewall? But now I'm telling you to shut it off? Yes, and it's usually fine, because most of you have a hardware firewall: that router that your computer plugs in to. That device is a firewall itself; you really don't need a software firewall at home if you have a hardware firewall.

Not sure what you have? Here's how to tell: do Start->Run and then type "cmd" (on older systems type "command"). That opens up a "DOS box", or "command window" as we old geeks call it. In that box, type "ipconfig". You'll get back something like this:

Windows IP Configuration

Ethernet Adapter Local Area Connection:
       Connection-specific DNS Suffix:
       IP Address....................: 192.168.2.4

(and more, but it's the IP Address we want)

If that number ( 192.168.2.4 here) doesn't begin with 192, 172 or 10, you don't have a hardware firewall, and you need to shut your computer off, get up, and run to the store to buy one. I'm not kidding: it's that important.

I've really glossed over this subject - firewalls are a very important part of Internet security - so important that the one I use costs over $900.00. But I have special needs; all you need for typical home use costs $50.00 or so. It's a small price to pay for what you get. Installation is simple and they come with full instructions.

- Tony Lawrence

The more geeky readers might enjoy The value of firewalls, whicch goes into this a bit more deeply.

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