It might seem like a good idea to have a little added protection, but when it comes to antivirus programs,  more is not better. You should never run two antivirus programs at the same time. They can interfere with each other, and may cause you more headaches than they cure. In fact, even having two antivirus programs installed on your computer at the same time can cause problems. So if you decide to change antivirus programs. Be sure to uninstall the first one before you install the new one.

The same holds true for firewalls. The rule is only use one firewall at a time.

However, antispyware programs are different. While you don't want to run two of them simultaneously, you may need to have more than one just to find all the spyware. I keep two or three on each of my computers. When you are ready to check for spyware, run one program and let it complete its work, then run the next one.

Be sure to keep your antispyware and antivirus programs up to date, as new spyware and new viruses appear every day.