This article really needs no introduction. There are many free anti-virus programs on the market, and you want to sort the wheat from the chaff. Fair enough. Documented here are the 10 best antivirus programs on the market.
While I won’t attempt to rank the programs here (in many ways the programs can’t be compared), I will attempt to give you an idea of under what circumstances they will be useful.
The order here for the 10 best antivirus programs  is mostly random, so be sure to read every entry if you want an idea of what will work for you.

Microsoft Security Essentials

Released by Microsoft in late 2009, Microsoft Security Essentials sports more than a typically verbose Microsoft name: it’s also a really good antivirus. Lightweight enough to run on older machines without crippling their performance, yet competent enough to handle most viruses and malware out there.
Perhaps the best part of MSE is its simplicity. As you can see, the user interface is really clear, with large buttons for the most basic functions. This is important if you’re setting it up on a computer for someone who is not computer-savvy.
Finally, MSE is completely free – there’s no professional version you can upgrade to. In fact, it’s even permissible to use in business situations, meaning you can use it at work without breaking the law. This alone sets it above most of the other selections for the 10 best antivirus programs.
Read more about MSE in Stefan’s article here or download MSE here.

AVG Free

This one recently topped our Movers and Shakers list of the top downloaded free anti-virus programs. But just because AVG is popular doesn’t mean it’s not great.
AVG has become synonymous with free anti-virus, and there’s a reason for this: AVG offers complete malware protection, with considerably less bloat than the top pay-to-use antivirus clients. And while AVG Free does constantly remind you that you could pay for the professional version of the program, it does this without ever getting in the way of the program’s core purpose: protecting you from viruses.
Though when it comes to upgrading one version of AVG to another, you need to make sure you’re good at reading what’s on screen, because the free download is only available via a tiny link at the bottom of the screen—the site really wants you to get the paid version. When upgrading to version 9 recently, for example, check out how hidden the free download was:
Not exactly a big link, is it? Figure this minor inconvenience out, however, and AVG is a a really good free anti-virus. Download AVG.

Avira Free

In terms of simplicity, Avira’s right up there with MSE. It’s fairly lightweight, too, so the comparison is quite apt. While Avira does have a paid professional version to peddle, much like AVG, it’s not quite as aggressive as AVG in peddling it. I’d say Avira is solid and worth looking into for sure. Download Avira Free here.

Avast! Free

If this competition were for the coolest name, the piratey Avast! would win hands down. Even though that’s not what we’re discussing, Avast! stands up pretty well. This is one of the top free anti-viruses on the market, and for good reason: it’s remarkably complete. Expect great all-around protection, including against trojans and spyware. You can also expect constant reminders that there’s a free version you can upgrade to, on your desktop and in your inbox. Still, the protection is solid.
Download Avast! here.

Malwarebytes

Whatever your default anti-virus is, you need Malwarebytes too. This program doesn’t run in your system background and constantly protect you, but when you run into a problem running Malwarebytes will usually take care of what other programs can’t. I’ve saved more than a few unbootable systems by running Malwarebytes from safe mode. This program takes care of any form of malware you throw at it, so keep it around. In fact, I’d keep this one on your flash drive in case you ever need to fix a computer for a friend (and if you’re reading this blog, you probably will).
Download Malwarebytes.

ComboFix

Consider this the nuclear option. If you know you’ve got a virus, but your usual anti-virus program can’t handle it, and Malwarebytes can’t handle it, it’s time for ComboFix. This program isn’t friendly: it runs from a command window and is proud of it.  And this is not a program you should use if you don’t know what you’re doing, because it can have devastating effects in the hands of the uneducated. But when all else fails, ComboFix delivers. Every geek should have this one on their keychain.
Download Combofix.

Clamwin

Clamwin is the Windows version of ClamAV, the main Linux anti-virus on the market. ClamWin is flawed in many ways: it simply scans instead of offering real-time protection, it doesn’t really do non-virus malware and it’s not exactly easy to use. Still, having ClamWin around doesn’t cost anything, and you can never have enough scanning tools in your arsenal.
Download ClamWin and see if you like it.

Panda Cloud AntiVirus

At first I thought the idea of a cloud-based antivirus was stupid, because it would only work while I’m online. Then it occurred to me: why the heck do I need an anti-virus when I’m offline?
As the name suggests, Panda Cloud Antivirus stores its virus definitions online. There’s an upside to this: your definitions are always up to date. There’s a downside, too, however: your anti-virus is constantly making use of your network connection.
I’d say this is a really good idea for underpowered PCs with constant access to the net. Like, say, a netbook. But if you’ve got a netbook you shouldn’t be using Windows anyway; switch to Jolicloud and you’ll have a functional netbook operating system immune to practically every virus.
Read a previously published article on Panda Cloud. Then download Panda Cloud Antivirus if you’re interested.

Comodo Firewall + Antivirus

Comodo is best known for its free firewall, but it also offers a bundled firewall and antivirus program. While the Comodo firewall isn’t the easiest to use, and the antivirus doesn’t include protection for non-virus forms of  malware, this one’s worth mentioning if you’re looking for a free security suite which includes both a firewall and anti-virus protection.
Download Comodo Free here.

Common Sense 2011

This one’s unusual in that it’s free and considered by far the best protection out there, yet can’t be downloaded anywhere. Without it, however, even the best security software is rendered useless.
If you haven’t already figured this out, Common Sense 2011 isn’t a product you can download so much as it is a state of mind. If you’re going to be free of viruses and malware you need to use your head while browsing the web. The most important thing to remember is this: if something sounds too good to be true, it probably is—and your computer will probably be compromised.
Free porn usually isn’t. Warez are best to be avoided altogether. Nigerians that need your help transferring money are never actually princes or princesses. You get the idea: avoid shady sites online and you’ll find you’ll get far less malware on your machine.

Conclusion

There are a lot of great free anti-virus programs out there, but what you use is mostly a matter of preference. Myself, I use Microsoft Security Essentials on my Windows machine because it’s free, lightweight and will never ask me for money. But I also make sure I always have Malwarebytes on my thumb drive for quickly removing viruses and malware from the computers of friends and family.
What about you? Which free anti-virus do you prefer? Commenting is good for you, so do so!