When pestilence or a virus strikes your castle, you've got to be prepared for a fight and ready to set up a quarantine. It's important to adhere to the standard practice of not downloading e-mail attachments or files from unknown sources, but that might not be enough. The most effective way to avoid viruses is with an often-updated antivirus program. Just as with antispyware applications, antivirus programs need to be updated to stay effective. For a great, free antivirus program, we recommend AVG Anti-Virus Free Edition. After an initial scan with AVG to check for immediate threatening strains, a great practice is to set up a regular schedule from within the program to make sure no new viruses invade your fortress. The E-mail Scanner and Resident Shield components of this app complete your castle's defense against malicious viruses.

Read a CNET editor's review of AVG Anti-Virus Free Edition.

Also, read more about how to use AVG Anti-Virus Free Edition.

Be sure to come back to the Download.com Security Center next month for extended reviews of the leading antivirus programs.

Once you have purged your castle of enemies, it's time to make sure some of the nastier ones can't even reach the walls. Spyware is by far the most pervasive threat on the Internet these days, and remaining vigilant in your fight is the best way to keep your system clean. A great way to stop spies before they reach your ranks is to catch them as they try to enter your castle. Though no programs are foolproof, we recommend Online Armor for its thorough safety-check setup process and real-time protection. During the initial setup for this program, you can select all the apps and components that are allowed to run on your computer. After a comprehensive scan, anyone who tries to gain access to your castle will be brought before you first. At your "Yea" or "Nay" decision, intruders will either be allowed in the castle or banished until you change your mind. Like your firewall, once you've trained Online Armor to recognize your most-used programs, you'll only be notified when a new spy is trying to gain access.