Avira AntiVir Personal Edition is my top pick if you're looking for the best protection against viruses. It is very light on resources and the detection rate of viruses and rootkits is outstanding, however, there are some reservations. First, it does not include antispyware protection or e-mail scanning, they are only available in the paid version. The lack of an e-mail scanner means that AntiVir won't warn you of infected emails before you open them. However, should you open an infected email, AntiVir will still spring into action, so it doesn't mean that you're not protected from email-based infections. Second, AntiVir's updates are usually slower than Avast and AVG, and occasionally stops updating for short periods of time due to server problems. Although AntiVir has advertisements that appear with every update, these ads can be disabled. Finally, AntiVir Personal Edition Classic has a time-limited license. It is renewable, but be aware that you'll have to periodically go through the hoops. Neither Avast or AVG is as effective in detection of viruses as AntiVir, but both are more complete products, and less intrusive in use.

Avast! 4 Home Edition is an excellent product for average users, in particular those who do not have a real-time antispyware product, although its funky media player style interface is not to everyone's taste. Avast is the least restricted product out of the three, with both anti-rootkit and anti-spyware capabilities. It also has full real-time capabilities, including a web scanner, an e-mail scanner and IM and P2P protection. In my usage of it, Avast was fairly light on resources. Avast is also the only one out of these three to continue support for older Windows platforms. However, Avast has a relatively high rate of false postives. It also requires periodic re-registration, whereas AVG Free does not. The sharware version also includes a script blocker, PUSH updates and various other features.

AVG Anti-Virus Free Edition has been continuously refined since it was initially released in 1991. The latest version makes further improvements to an already solid product. It now includes spyware, phishing, and email scam protection. Its detection rate is still very good. Regular automatic updates come quickly as before and, despite rumors, the new email scanning feature is not trial limited to 30 days. It has grown considerably in size, is heavy on resources and has very slow scan speeds. The automatic updates occasionally did not work on my computer. By default, it installs the AVG Security Toolbar with Yahoo search. Free and paid versions are available; the differences are that the free version has anti-rootkit disabled, provides Linkscanner Lite instead of Linkscanner Pro and has no technical support other than a free user forum.

These are excellent free antivirus that provide a real alternative to the major antivirus software.

You can increase your protection if you run on demand scans with another antivirus. On demand scans can be run regularly to check for viruses and other malware that may have been missed by your main scanner. If you have a good preventive security strategy in place, however, the extra protection this offers is minimal.

Obviously, if you disable the real-time protection of AntiVir, Avast!, or AVG they can be used as on-demand scanners.

Kaspersky Virus Removal Tool is an excellent on demand scanner, with good detection rates and strong removal capabilities. However, it requires you to download the whole file again if you want to update it. Also, bear in mind that the detection won't be as good as the current Kaspersky products, which has a newer engine.

Dr.Web CureIt! is also an excellent choice as an on demand scanner. It is a portable application and has strong removal capabilities. However, it suffers from the same flaw as the Kaspersky AVP Tools - it cannot update. Also, Dr.Web has not been scoring that well in recent tests. Nevertheless, it is still a good choice as a secondary/tertiary on-demand scanner.