Updated April 2014
One nasty virus could expose your financial information or stop your computer from working at all. What you need is the best antivirus software possible on your computer. Luckily, some of the best are also completely free!
Many companies offer free versions of their popular antivirus programs for home users. My favorites are avast! Free Antivirus, AVG Anti-Virus Free, and MSE (in that order) but be sure to look through the alphabetical list below to find the best free antivirus for you.
Important: I've included no trial or shareware antivirus programs in this list. These are the best antivirus programs that are completely free and work similarly to, or better than, expensive programs from companies like Norton and McAfee.
See my Free On-Demand Virus Scanners list if you're interested in free antivirus tools without constant virus protection or my Free Online Virus Scanners list if you're interested in a free online-based antivirus scan of a file. See this Free Bootable Antivirus Tools list for virus scanners that don't even need a working computer to be used.
Lavasoft's Ad-Aware Free Antivirus+ program is different than the "Ad-Aware" you may already be familiar with. This program is a true, always-on, completely free antivirus program.
Ad-Aware Free Antivirus+ supports Windows 8, 7, Vista, and XP.
If my list was anything other than alphabetical, Ad-Aware Free Antivirus+ probably wouldn't head up the pack, mainly because email scanning isn't supported. However, if you love Lavasoft's other free products, Ad-Aware Free Antivirus+ is a pretty solid choice.
Amiti Antivirus is a free antivirus program that includes heuristic scanning and supports 4 different scan types, including one that can check for viruses that are currently running in memory.
Amiti Antivirus can be used with Windows 8, 7, Vista, and XP.
I really like how easy Amiti Antivirus is to use. All the settings and options are organized on the left side of the program in their respective areas without being overly cluttered.
There's also a tool included in Amiti Antivirus that can be used to quickly clean temporary system and Internet Explorer files to free of disk space.
AVAST Software's avast! Free Antivirus 2014 most certainly deserves to be on any list of the best free antivirus programs. avast! Free Antivirus has fully functioning antivirus and antispyware engines protecting your PC from threats from the Internet, your files, emails, and even instant messages.
avast! Free Antivirus 2014 (version 9) supports Windows 8, Windows 7, Windows Vista, and Windows XP.
One big reason I included avast! Free Antivirus 2014 as a best free antivirus program is because of its "heuristics engine" which can detect previously unknown viruses and other malware. I also like the fact that AVAST has been making this antivirus product since 1988 and is often cited as the most installed antivirus product.
AntiVirus Free 2014 from AVG is one of the best free antivirus software tools available and is probably my personal favorite.
AVG AntiVirus Free is a full-fledged antivirus and antispyware tool, includes an email scanner, link scanner, scheduled scanning options, automatic updates, and more. There is no need to pay for an antivirus program when one this good is just a download away.
AVG AntiVirus Free 2014 works on Windows 8, Windows 7, Windows Vista, and Windows XP.
The huge number of premium features, frequency of updating, and install-it-and-forget-it aspect of AVG's AntiVirus Free 2014 really do make it one of the best of the best free antivirus programs available today.
Avira Free AntiVirus protects you from viruses, Trojans, worms, spyware, adware, and various other kinds of malware, making it a fully functional antimalware tool and certainly one of the best free antivirus programs.
Avira Free AntiVirus (version 14) works on Windows 8, Windows 7, Windows Vista, and Windows XP. Avira can also be used on a Mac and Linux computer.
The scope of malware that Avira Free AntiVirus can keep you safe from is alone enough to make it one of the best free antivirus software programs but the heuristics and ease of use add to its value too. The only things I didn't like about Avira Free AntiVirus was the configuration you have to complete after installation which might be intimidating if you're a computer novice.
Bitdefender Antivirus Free Edition is on par with any of the arguably better-known free antivirus programs in my list.
Bitdefender Antivirus Free Edition is incredibly easy to setup and configure, uses very little system resources (it won't slow down your computer), and doesn't constantly suggest that you upgrade to their premium offerings.
Antivirus Free Edition by Bitdefender fully supports Windows 8, Windows 7, Windows Vista, and Windows XP.
The sheer simplicity of Bitdefender Antivirus Free Edition, both during installation and use, make it, in my opinion, one of the better of the best free antivirus programs.
Baidu Antivirus 2014 is lightweight and fights malware via its cloud-based virus database.
Baidu Antivirus 2014 (version 4.4) works in Windows 8, Windows 7, Windows Vista, and Windows XP.
Install Baidu Antivirus 2014 alongside other antivirus software for increased protection. It automatically updates, scans USB devices and the Windows registry, and has a built-in cloud file scanner to upload suspicious files to Baidu to be scanned.
Overall, Badiu Antivirus 2014 ran quickly, using little system resources, and seemed to function similar to the other antivirus programs in this list.
Comodo Antivirus 6 from Comodo Security Solutions is another excellent program, easily one of the best free antivirus options out there. Comodo Antivirus 6 protects you from several threat sources, just as most of the other free antivirus programs on this list do.
Comodo Antivirus 6 works on Windows 8, Windows 7 and Windows Vista.
Comodo Antivirus 6 ranks as a best free antivirus solution almost solely because of its Defense+ technology that, by default, assumes unknown files are threats instead of safe. That sounds like it might cause problems but Comodo Antivirus utilizes some other technologies to make the whole process silent but still very effective.
FortiClient is an antivirus, web filtering, firewall, parental control, optimization, (and then some) program that's powerful enough for a business to use. It's more accurately referred to as a "threat management" tool.
FortiClient 5 works on Windows 8, Windows 7, Windows Vista, and Windows XP.
While that might all sound really complicated, especially considering that you probably only have one computer you're worried about, FortiClient is really easy to setup, automatically updates its virus definition files, does a full system scan once per week, and much more, all without you ever having to worry about it.
Immunet FREE Antivirus 3 is a unique, cloud-based antivirus program, much like Panda Cloud Antivirus and Kingsoft Antivirus. Immunet FREE Antivirus 3 protects your computer from bots, worms, viruses, Trojans, keyloggers, and spyware.
Immunet FREE Antivirus 3 works on Windows 8, Windows 7, Windows Vista and Windows XP. You must be connected to the Internet at all times.
I think FREE Antivirus 3 from Immunet is one of the best free antivirus programs for several reasons: you never have to update it, it has completely free telephone based support, and it can be run alongside some of the other best free antivirus tools in this list, increasing your overall protection.