Keeping your Windows computer virus-free doesn't have to cost you a lot of money. Heck, it doesn't need to cost you any money. There are plenty of good options available for those of you on the hunt for free antivirus software. Two things to keep in mind: First, a number of the developers offer a non-free version on the free version's download page via a service called TrialPay. The totally free version is normally on the left, the TrialPay offer on the right - make sure you're clicking the link you actually want. Second, as with other free software, some of the developers ask for support in the form of a toolbar install. They're all optional, so make sure to un-tick the checkboxes during the install if you don't want the toolbar.
avast! is an antivirus set that is able to detect the presence of viruses in computers. It has a powerful antivirus kernal that has a boot-time scan, improved resident protection, heuristic analysis for email, and a script blocker. The program works great as a on-demand and/or resident virus scanner. The skinable interface is easy to use for any user.