Test your Defenses Online

<< Scan your computer to see if it's already infested with malware.

Beware: Free scan sites may *find* malware on your PC or holes in your defense and offer to fix your PC, usually by selling you a program. Don't buy any solutions until you have checked the recommendations in the 7-Step Plan, particularly Step 4: Install Anti-spyware/Anti-malware Programs.

Hint: Use Microsoft's monthly "Patch Tuesday" (automatic updates) to remind you to run online scans. :-)

Comprehensive scans

Use Panda Security's comprehensive, new ActiveScan to see if your computer is infected with any of the more than 3 million malware microbes there are out there. (You may need to use Internet Explorer to run this test, as it wouldn't run when I tried it with Firefox.) :-(
Scan your computer for security status and other maintenance factors at the "Microsoft Live" Security Center.
Secunia will check your computer online to see if Windows and other internet-facing software is fully patched. Update: Secunia now offers a [free] "Personal Software Inspector", which worked better for me. The only drawback is that you need to download and install it.
Scanit checks your browser for various security problems.

Various security tests

Simple tests: Get a feel for how your anti-virus program would handle a real virus. These tests use a standard "dummy" virus that all anti-virus programs should recognize.
Panda Software: Use their simple tests to see how well you your antivirus program is set up to protect you. (free).
GFI Email Security Testing Zone: Easy but comprehensive testing of your email security. Find out if you are vulnerable to any or all of the 11 most common email threats, including viruses, worms and other malware.

Firewall test sites

Firewalls do most of their work with little fanfare. How do you know yours is actually working? You can't tell unless you test it. You can't test it directly, because the tests must come from outside your computer. You need to find a test site that will rigorously challenge it.

"Shields Up!!" at GRC.com (Click the "Shields Up" logo.) The first test site that I discovered. It's still the one I have most confidence in. Steve Gibson understands the nitty-gritty of Internet packets, which is where hacking begins.
BroadbandReports.com is another reputable firewall scanning service.
The "Sygate" site is easy to navigate. Sygate tests take several minutes to run, so I assume they are fairly thorough.
"SecuritySpace security audits, also known as network vulnerability assessments, provide the web's most cost-effective, comprehensive, full disclosure audit service available." Highly recommended.
You will find these sites and more at http://www.dozleng.com/.

Firewall tests only show the view from the outside looking in. If you have a resident Trojan, it can easily create a hole in your firewall and "call home". Once it establishes contact with it's Trojan master, your computer is completely open to attack. (Go on to the next section to learn how to test for Trojans.)