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.
License: FreeLanguage: English
OS: Win XP/Vista/7
Avira Free Antivirus
Avira AntiVir Personal provides basic protection against viruses, worms, and Trojans, and also has basic anti-spyware protection. Avira claims the application monitors all user activities on the system for maximum pro-activeness.
Support is handled through an online support forum. An FAQ, tutorials/install guides, and documentation are all provided. This is essentially the same way AVG handles support for its free antivirus suite.
License: FreeLanguage: English
OS: Win XP/Vista/7
Bitdefender Free Antivirus
BitDefender Free Edition is a free anti-virus software developed by the SOFTWIN, a Bucharest-based company. BitDefender Free Edition was designed with a centralized management console, which allows protection options configuration for all BitDefender modules. Its Live Update module ensures hourly updates of the program and virus database. Automatic and manual update are available. Intelligent update of antivirus protection, without your intervention. The update can be done from the network over the Internet, directly or through a Proxy Server. This function also repairs the software by automatically downloading and replacing the damaged program files and other components.
License: FreeLanguage: English
OS: Win XP/Vista/7
Pc Tools Antivirus
PC Tools AntiVirus Free Edition will protect you against the most nefarious cyber-threats attempting to gain access to your PC and personal information. Going online without protection against the latest fast-spreading virus and worms, such as Netsky, Mytob and MyDoom, can result in infections within minutes.
License: FreeLanguage: English
OS: Win XP/Vista/7
Clamwin Antivirus
ClamWin is free, opensource antivirus software. I've been using it for a couple of years now and have found it to be very reliable. The software stands true to its promise that virus definitions are updated regularly - I notice updates on a daily basis. Virus definitions can be updated automatically or manually via easily configurable options.
License: FreeLanguage: English
OS: Win XP/Vista/7
Comodo Internet Security
Comodo is a Network Product Work Hot Companies Awards 2009 finalist and their latest product, Comodo Internet Security, is a no-cost full security package, incorporating an antivirus program with a firewall, and a strong customizable defence system called Defense+.
The truly outstanding feature of Comodo Internet Security is the ease of installation and setup. There is limited amount of jargon, and changing the settings of the application does not involve a detailed trek through each of the menu options. The application is distinctly user-friendly.
Comodo Internet Security is available in Free and Pro versions.The Free version will probably meet most people's needs, but see this page for an explanation of the differences.
License: FreeLanguage: English
OS: Win XP/Vista/7
Microsoft Security Essentials
The latest addition to this list, Security Essentials is the free follow-up to Microsoft's popular OneCare. While it's a very basic antivirus program, it provides a very good level of protection without bogging down your system. Like the other titles on this list, SE updates automatically and it can also perform scheduled scans as often as you like.
It's still a beta release, but is very stable and I've not noted any problems with it so far.
License: FreeLanguage: English
OS: Win XP/Vista/7
AVG Free Antivirus
AVG Technologies is best known for antivirus protection, but in recent years the company has branched out, adding system tune-up, parental control, online backup, and more. But have no fear; you can still get the powerful protection of AVG Anti-Virus Free 2012 without spending a penny. In my tests and in tests by independent labs it beats many of its for-pay competition. Do note that it's specifically free for personal use; business users must pay for AVG's antivirus protection.
License: FreeLanguage: English
OS: Win XP/Vista/7