Windows has more antivirus programs than we can count, but we keep coming back to Microsoft's own offering, Security Essentials. It's easy to use, lightweight and does everything in the background, so you rarely need to interact with it.
- An extremely easy to use interface from which you can manually update definitions, see your recently detected items and schedule scans
- Set the default action for different alert levels (i.e. remove or quarantine the offending file)
- Real-time protection that scans all your downloads, monitors file activity and more.
- Exclude certain file types, locations and processes from a scan
- An heuristic scanning engine that helps it detect viruses not in its definitions
Microsoft Security Essentials solves every problem you've ever had with antivirus. It's super-lightweight, easy to use, and will update and scan without you ever knowing it was there. Its interface is dead simple to use, so you can set up schedules and change your settings when you want, but you really don't need to do much. Set it up, forget it and stay protected. It's amazing it took antivirus apps this long to get this simple.
MSE's only real downside is that it while it's pretty darn effective, it isn't the most effective program at catching viruses, at least according to AV-Comparatives' report. Still, it's one of the most effective programs out there, especially among free programs, and coupled with a bit of common sense, should keep you more than protected from any malware floating around the net. It also doesn't have any email, IM or other extra scanners, but we personally consider a lot of those things bloatware. There's a fine line between feature-filled protection and something that's just going to slow your system down more than a virus would. Practice safe browsing and emailing and you'll get the best of both worlds.
When it comes to free options, Avira is probably the best competitor to Security Essentials. AV-Comparatives found it to be the most effective free program out there, at least with heuristics set to "high" (which isn't without downsides, mainly a higher possibility of false positives). Like Security Essentials, it isn't super feature-filled, and it isn't nearly as lightweight as Security Essentials either (nor is the interface as easy to use). If you prefer something a tad less aggressive, ESET NOD32 is a great application that's almost as simple as Security Essentials, though not quite. All three of these are great options for free antivirus.
We'd be remiss not to mention Avast and AVG, two long-time favourites of our readers. However, both have quirks that make it hard for us to recommend them over the above options -- they aren't quite as effective in finding viruses and malware, and both have their own bloat and annoyances (like Avast's once-a-year registration requirement) that put them at the bottom of our list.
Some paid alternatives, like F-Secure, Norton and McAfee Total Protection are better at finding viruses and malware than free options, but they do so at the cost of your system resources (and your wallet). We personally don't think they're necessary in a home setting, as long as you use good browsing habits, but if you want to protect yourself against every possible virus or theoretical piece of malware you could get, they might be the way to go.
In the end, the best possible antivirus you can have is good browsing practices (you know, in case I haven't mentioned that enough). They're more effective than any antivirus software out there, and they won't put any kind of drain on your system resources, money, or stress level. Keep Windows and applications like Flash updated, stop downloading questionable files, and just practise good common sense. If you do, you'll probably have to deal with your antivirus program very little.
There are more antivirus programs out there than we can even count, but these are probably the best out there right now. Many of you undoubtedly have your own favourites, some that we might not have even listed -- so share your favourites with us (and why they're your favourites) in the comments. If you're interested in more comparisons between each program's effectiveness, we highly recommend checking out AV Comparatives' summary report from last year. It has a wealth of information for those looking to install antivirus on their system.