Without antivirus protection, a Windows machine is a ticking time bomb. Of course, there are hundreds (if not thousands) of possible antivirus solutions for the Windows operating system. Some are worthless and some are viruses themselves. But others are pretty darned dependable. I wanted to share my favorite free real-time antivirus solutions for the Windows operating system. You might already have a favorite, but it’s always good to have another option in your back pocket. Just remember to have only one installed at a time.

1: Avast Free

For the longest time I recommended AVG Free to clients. That time has come and gone. Now, when a client needs a free go-to antivirus software package, I always recommend Avast Free Edition. Avast has a ton of features for a piece of free software. But more important, it does a great job protecting PCs from those nasty infections. It also does a good job blocking spyware. The free version is limited to virus and malware protection, but what more do you need? Well, if you need online protection (such as safe shopping), ID protection, and advanced firewall, you’ll need to drop some coin for the professional version.

2: Microsoft Security Essentials

If you or your clients are looking for a bare bones antivirus solution that does one thing and one thing only (but does it very well), download and install this outstanding free Microsoft product. What I really like about Security Essentials is that once installed, it’s unobtrusive. You will hardly know it’s there. Unlike some solutions that bring your machine to a grinding halt, Security Essentials uses little CPU and can do a scan without your even realizing it’s happening. Security Essentials is also one of the easiest to install, configure, and use. So for those less-than-savvy end users, this might be the one you want.

3: Avira Free Antivirus

Just two clicks to install, and your machine has some basic, yet solid antivirus protection. No, Avira Free will not protect you from phishing like its premium brother. Nor does it have a gaming mode like its premium upgrade. But Avira Free will do a great job of protecting your machine from viruses, with an easy-to-use interface and an incredibly fast scanning engine. In fact, this might well be the fastest antivirus scan you will ever use. What I like about this entry is that it checks for viruses, Trojans, AND rootkits. Not many free antivirus solutions go that far.

4: BitDefender

BitDefender is one of those solutions that few know about but more should. It’s an outstanding solution that has the standard features (virus scan/removal, scheduled scan, immediate scan, quarantine, reporting). It’s one of the on-demand solutions. BitDefender does not include any real-time features but makes up for it with a strong scanning engine that can be scheduled for use at any time. What I like about on-demand scanning is that it doesn’t interfere with email or Web browsing. When push comes to shove, I always trust the BitDefender line of tools — and the free version is no exception.

5: Comodo Antivirus

Comodo Antivirus is probably the least well known tool on this list, but that doesn’t make it a lesser product. In fact, it could be a strong solution if you’re looking for guesswork-free protection. Comodo automates the decision-making process for blocking or allowing trusted or untrusted files. If anything is questionable, it’s sandboxed for your examination. Comodo tracks and protects from malware as well as viruses. And with an adjustable security level (via a simple-to-use slider), it’s easy to modify the level of protection you want on a desktop. Comodo was also designed with optimization in mind. Although not as unnoticeable as Microsoft Security Essentials, Comodo does do a great job of remaining in the background.

Other options?

Everyone has his or her opinion, and when it comes to antivirus solutions, those opinions can get rather heated. Do you agree with my choices for antivirus? If not, what are your picks? What’s your go-to free AV tool?