How good is Microsoft's free antivirus software?

Microsoft has officially unveiled its long-awaited consumer antivirus offering. Formerly code-named “Morro,” it’s now been christened Microsoft Security Essentials, and it will enter public beta testing next week. If you have a licensed copy of Windows XP (Service Pack 2 or above), Windows Vista, or Windows 7, you’ll be able to download and install the software at no additional charge. No subscription is required for ongoing definition updates, either. The final release is scheduled for this fall.

The public beta will be limited to 75,000 downloads, Microsoft says, and the targets are global. The initial beta release is limited to the United States, Israel (where a core development team is based), and Brazil. Next month, the beta will open up for users in China. It’s no coincidence that Microsoft is rolling out early in Brazil and China, which are large-scale vectors of malware infections because of the sheer number of Windows users running without antivirus protection. According to Microsoft, barriers to adoption of paid security software are especially high in developing markets, where internet access is slower and credit cards are unavailable to a large percentage of the population.

The MSE download is impressively lightweight. The x64 copy I installed on Windows 7 was 3.8 MB in size; x86 copies are 4.8 MB for Vista/Windows 7 and 7.7 MB for Windows XP. Installation (including the most recent definition updates) took less than four minutes and, as promised, the initial setup didn’t require any personal information or registration. After I accepted the license agreement, the software informed me that it needed to update its virus definitions and then proceeded to get the most recent updates on its own.

You can bet that the beta release will be seriously tested by independent labs and especially by Microsoft’s for-profit competitors in the coming weeks. If it has any weaknesses, expect to see them heavily publicized. Meanwhile, I’m sufficiently impressed by MSE in operation to give it a more in-depth workout on multiple systems here.