Currently there are three good free anti-virus programs out there. They are Alwil Avast! 4.6, AVG 7 and Anti-Vir. I would advise not to use Anti-Vir, as it doesn't scan e-mails, which is one of the most popular ways of distributing viri. The real battle is between Avast! and AVG as they both have similar detection rates according to the Virus Bulletin, an independent virus testing organisation. Avast! has a better track record than AVG, but Avast! also requires more memory to run which can be a problem for systems with less than 256MB. AVG has also released a new version 7, which many users have had issues with including updating problems and the removal of viri. Ultimately, either anti-virus product will suffice as they both scan for in the wild and on-access. To make Avast! use less memory, you can also disable protection that you don't use, like if you don't use MSN Messenger, you can disable that protection.
The commercial product Norton Anti-Virus has been dubbed 'blotware' because it takes up lots of memory and files take longer to be processed. It may be a massively biased opinion, but most people in the know dislike Norton products because of the resources they waste.
Three firewalls all contending for first place of best free firewall: ZoneAlarm Free, a trusted and popular program, Kerio, which has stopped being freely updated and Sygate Personal which has more features than any other firewall. Each of these firewalls do what they're meant to, and that is to block unallowed outbound programs from accessing the Internet while also monitoring inbound traffic. No program will be allowed to access the Internet without your explicit permission when any of these firewalls is active. The most popular firewall is ZoneAlarm free, because it works straight away, but that isn't to say that Sygate is worse.
In addition to these software firewalls, a hardware firewall, found in many routers, also provides protection but its best with broadband to have both a hardware and software firewall active.
This category is a bit different. There is one prevention tool called Spyware Blaster which creates entries in your registry to recognise when a blacklisted program or cookie attempts to be installed. The installation will never continue if it is malware or spyware that Spyware Blaster recognises so it is important to update the program often. To eliminate the spyware / malware or usage tracks from your computer, you need to use either tool of Spybot - Search and Destroy or Lavasoft Ad-aware. S&D has many helpful tools that come with it and is completely free of advertising so I would recommend it.
Microsoft has also released an Anti-Spyware tool (formerly GIANT Anti-Spyware), but this isn't looking to good in its current beta stage. If you have it uninstall it and replace it with one of the ones mentioned above.
With Spybot Search and Destroy's extra tool, it's easy to remove spyware.
You can read more about a bunch of spyware removal programs in an article we published called "Spyware and Adware Removal Guide - Speed Up and Free your PC" back in October 2004.
How much to upgrade to x64 Edition?