Computer security has become a major problem for most users but you'll find plenty of help and advice at these top sites.

Good Spyware Resource Site
The current spyware/adware/scumware plague is reaching near epidemic proportions. This free site offers an excellent set of protection/removal tools and many other resources.
http://www.mvps.org/inetexplorer/Darnit.html

Good Malware Prevention and Removal Site
Here you can find excellent advice on how to configure your system to reduce the chance of spyware infection plus detailed information how to remove an existing infection. Most of this information is available elsewhere but the site owner Shanmuga has done an excellent job compiling the information and making it accessible. Well worth visiting and bookmarking.
http://www.malwarehelp.org/

How to Remove Spyware (And Other Nasties) from Your PC
This practical guide is as good as I've seen but it's not suitable for newbies.
http://www.michaelhorowitz.com/removespyware.html

Help for Spyware You Can't Remove
Some spyware just keeps on re-appearing on your PC no matter how many times you remove it. When this happens, download HijackThis from this page and follow the instructions. The page also shows you how to post the output from HijackThis to the Tom Coyote web forums. These folks should be able to help you permanently get rid of the problem. It won't cost you a cent either.
http://www.tomcoyote.org/hjt/

Run Online Virus Scan from Both Internet Explorer and FireFox
I've mentioned elsewhere the excellent Trend Micro online virus scanning service but lamented the fact that the service utilized ActiveX and consequently could only be accessed through Internet Explorer. Thanks to Terry Smith who sent me a non-ActiveX link where you can run the Trend scan using FireFox or indeed any browser that supports Java. It's well worth bookmarking as this is one of the few online scans that will also remove infections rather than just detect them.
http://housecall.trendmicro.com/

Spyware Removal Utilities That Are Actually Spyware
A few issue back I mentioned a number of bogus spyware removal utilities, many with names deceptively similar to well known legitimate products. This site has a more complete list with over 100 entries. Many of the "free" apps generate large numbers of fake "infections" to alarm users into purchase. Others are simply spyware applications. Proof positive that scumware comes from scums.
http://www.spywarewarrior.com/rogue_anti-spyware.htm

Free Service Tests a Suspicious File
Got a program you'd like to run but not sure if it's kosher? Then upload it to this site where they'll run it through 13 different virus scanners and let you know the results.
http://virusscan.jotti.org

How to Test Your Email Security
A while back I mentioned these two sites that will send you a series of email messages, each of which tests for a specific known email vulnerability. The messages are quite safe so don't be alarmed if your virus scanner gives a warning. In fact, only get alarmed if your virus scanner doesn't give a warning!
http://www.gfi.com/emailsecuritytest/

How to Improve Your Internet Security
This site offers some excellent security advice for experienced users. I particularly liked the suggested settings for enhancing  the security of Internet Explorer.
http://surfthenetsafely.com

Home of the Hacks
Trying to keep track of the security problems with various software products?  This page will help you. While visiting, check out their user survey of the top security tools.
http://www.insecure.org/

Computer Security Tips
The International Computer Security Association has a Web site with lots of papers, pointers and other useful information for anyone involved in IT security issues.  Well worth a browse.
http://www.icsa.net/

Popup Stopper Wars
How well does your popup stopper rate? Find out by running the tests at this site. The site also rates a range of freeware and commercial popup stoppers. The top performing free product was EMS Free Surfer, a product I'd never heard of.
http://www.popuptest.com
http://www.emsproject.com/FS/ <= EMS Free Surfer

Great Security Resource for End-users
If you haven't the patience to answer beginners’ questions about computer security, you can refer them to this excellent resource site. Experienced users should check it out, too.
http://www.cert.org/homeusers/HomeComputerSecurity/

Comprehensive Vulnerability Database
OSVDB is an independent security vulnerability database that is free for all to use. It's large, up-to-date and comprehensive in its operating system coverage.
http://www.osvdb.org/

Spam Haters Unite
The coalition against unsolicited commercial email has a site where you can find tips and techniques for blocking spam.
http://www.cauce.org/