Microsoft Security Essentials (MSE) was created by Microsoft because many Windows computers were unprotected with outdated anti-malware products. Many new PCs come with time-limited security programs so many users believe they're protected even though the initial subscription period may have ended. Some don't even activate the free, bundled solutions at all.
MSE is easy to install and use. MSE is small and light and runs quietly in the background. It's absolutely free as long as you have a genuine copy of Windows XP, Vista, or Windows 7. There's no registration, no annual fees. You install it and forget it, and it keeps you safe.
MSE is updated when needed and delivered through Windows Update. Microsoft publishes new malware signature updates three times each day. None of it impacts the user at all. You just install it and forget it.
Windows guru Paul Thurrot concludes in his review:
"There's been a lot of interest in Microsoft Security Essentials and I think it will prove quite a hit with users. It's free, effective, lightweight, and quiet and is, in other words, exactly what I'm looking for in a security solution. And it comes with no strings at all. As long as you're running a genuine Windows version, you can install this product without worrying about up-sell advertisements, yearly renewals, or other silliness. And you can do so on as many Windows-based PCs as you own. I'd like to see it just included with Windows, but what the heck: Free and easy is the next best thing. Microsoft Security Essentials is highly recommended, to all Windows users." -- Paul Thurrott September 29, 2009
If you don't wish to spend the money on dedicated security software like NOD32, BitDefender, Spysweeper or Spyware Doctor, then Microsoft Security Essentials is a good alternative. If you're already using free software like AVG or Microsoft Defender, then a switch to Microsoft Security Essentials would be a good idea.