In my last column, I gave you some good downloadable antivirus alternatives to protect your PC. One thing I probably should have said (after reading the comments) is that the most important criteria for picking an antivirus program has more to do with whether the company is alive and well and provides important and regular updates. If you use Norton, you're probably OK. That's also true for McAfee. These companies stay on top of updates, and they're not going anywhere. The programs I listed were my picks for reliable shareware (and free) antivirus software that you could use right away.

--> With that said, having a good virus program is not enough to stop all intruders. Another extremely important line of defense is a firewall. Some might say that you need a hardware firewall (as a function of your router, for instance) to keep intruders away from your system. For most people (me included), a good software firewall offers plenty of protection against attacks and also against software on your hard drive that might be trying to contact "the mothership" without your knowledge.

Like the antivirus programs I mentioned in the last article, software firewalls usually have a limited free version that works perfectly well on its own. If you want the extra features offered by the paid version--such as e-mail scanners, chat client security, pop-up blockers, and other features--you'll have to pay for the full version. I've found that most of the extras are obtainable elsewhere for free. The bottom line is, having the free version of a firewall program and the added line of defense it provides is much better than having nothing at all. I strongly recommend that everyone who doesn't have a firewall at least get one of these software firewalls on their machine for the protection they give.

ZoneAlarm is one of the more well-known firewall programs, and it's the one I run at home. It installs easily and alerts you via a pop-up window the second anyone tries to access your connection--in or out. A paid version of ZoneAlarm offers more options, but the free version is enough for basic security, which is why I'm listing this one as free. (Free/Windows)

Kerio Personal Firewall is another solid firewall program that provides protection similar to ZoneAlarm's. I like how this program essentially "fingerprints" trusted programs so that Trojan horses that impersonate other programs have no chance of squirming in. Kerio Personal Firewall has both paid and free versions like ZoneAlarm does, and the free version works great.(Free/Windows)

NetVeda Safety.Net is a fairly recent discovery for me, but so far, I like what I see. Like ZoneAlarm and Kerio, this app lets you designate safe apps and keeps a close eye on what's trying to get through. My one problem with this one is that some of the notifications are pretty unidentifiable unless you really know your stuff. For that reason, this one might be more for advanced users. (Free/Windows)

The free version of each of these firewall programs offers plenty of protection for most users. If you don't already have a firewall through a business network or at home, I strongly suggest you download one of the programs above.