1. Ad-Aware Free Antivirus+
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.
2. Amiti Antivirus
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.
3. avast! Free Antivirus 2015
AVAST Software's avast! Free Antivirus 2015 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.
4. AVG AntiVirus Free 2015
AntiVirus Free 2015 from AVG is one of the best free antivirus software tools available and is probably my personal favorite.
5. Avira Free Antivirus
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 works on Windows 8, Windows 7, Windows Vista, and Windows XP. Avira can also be used on a Mac and Linux computer.
6. 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.
7. Baidu Antivirus 2015
Baidu Antivirus 2015 is lightweight and fights malware via its cloud-based virus database.
Baidu Antivirus 2015 works in Windows 8, Windows 7, Windows Vista, and Windows XP.
8. Comodo Antivirus
Comodo Antivirus from Comodo Security Solutions is another excellent program, easily one of the best free antivirus options out there. Comodo Antivirus protects you from several threat sources, just as most of the other free antivirus programs on this list do.
9. FortiClient
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.
10. Immunet FREE Antivirus 3
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.
11. Kingsoft Antivirus 2012
Kingsoft Antivirus 2012 is a cloud-based antivirus program like Panda Cloud Antivirus and Immunet FREE Antivirus. Kingsoft Antivirus keeps an eye out for malware locally, when downloading files, while chatting on IM, and more.
12. Microsoft Security Essentials (MSE)
Security Essentials from Microsoft is definitely one of the best free antivirus programs available right now. Microsoft is relatively new to the antivirus game but don't let that scare you - Security Essentials is a fantastic antivirus program that protects you from all sorts of malware, updates automatically, and is incredibly easy to use.
13. Outpost Security Suite Free
Outpost Security Suite Free is a free antivirus program that supports web and email scanning as well as a firewall.
The built-in firewall can control applications and network packets through a filter as well as local network policies.
14. Panda Cloud Antivirus FREE
Panda Cloud Antivirus FREE protects you from several kinds of malware threats - viruses, worms, Trojans, adware, and more - just like all the other free antivirus programs in this list.
What makes Panda Cloud Antivirus FREE one of the best free antivirus programs is that it does its job from "the cloud" meaning the hard antivirus work that typically slows down a computer is done on computers elsewhere on the Internet, freeing up your computer to work like it should and protecting you from malware even better.
15. Rising Antivirus Free Edition
Rising Antivirus Free Edition is the free antivirus offering from China's largest antivirus maker, Rising Software.
Rising Antivirus Free Edition works with Windows 7, Windows Vista, and Windows XP.
16. UnThreat Free AntiVirus 2014
UnThreat Free AntiVirus 2014 offers standard malware protection, including threats via email. I found nothing too impressive about this program aside from its price... or lack thereof, I suppose.
UnThreat Free AntiVirus 2014 works in Windows 8, Windows 7, Windows Vista, and Windows XP.
17. Zillya! Antivirus
Zillya! Antivirus is another free antivirus program that works with Windows. It's nearly the same as most of the other programs from this list.
It actively scans emails and USB devices, and you can choose a quick, full, or custom virus scan. There's an exclusions category so you can remove certain folders and/or files from being scanned.
18. ZoneAlarm Free Antivirus + Firewall 2015
ZoneAlarm Free Antivirus + Firewall 2015 is just that - a combination free antivirus and firewall tool.