If you want a strong security foundation, you'll need sturdy walls to keep invaders out. The first line of defense against would-be attackers on your computer system is a strong firewall program. With a good software firewall you can monitor all of the transmissions sent or received by your computer. One of the best free programs is ZoneAlarm. With this application installed, you get always-on protection from threats. In fact, while using ZoneAlarm, most invaders storming your walls will need to ask your permission to enter. Once you've trained ZoneAlarm to accept common connections (like chat clients and Web browsers), you'll only be notified when the bad guys come knocking.

One of the last things you want when trying to keep your castle safe is spies exporting information to their dastardly cohorts. To keep spyware from accessing your computer, you need to monitor your ranks (and files) thoroughly and often. Finding all the spyware on your computer is a difficult task, so we recommend using two programs for this job. Consistently one of the best in the antispyware category is Ad-Aware SE Personal Edition. With this program installed and properly updated, you can scan your system for spies and banish them from your computer. Your defense shouldn't stop there. Since antispyware developers update their spyware definitions at different times, it's best to check more than once to see if any of the more malicious traces got past first inspection. As your secondary spyware program, SpyCatcher Express 2006, Microsoft Windows Defender, or McAfee AntiSpyware are all solid choices. With a regular schedule of scanning and removing spyware threats using at least two programs, you can rest assured there are no sneaky spies in your midst.

For a full collection of antispyware products with CNET editors' reviews, see our Ten Top Spyware Killers feature.