Security Essentials' user interface is particularly straightforward--perfect if you don't want to waste time messing around with your antivirus software.

Microsoft's program cleans up malware infections quite effectively: In our tests, it identified all active infections on our machine and disabled over 93 percent of the malware. It removed all traces of malware 80 percent of the time--better than any of its competitors in this roundup. In addition, it was one of the two free antivirus applications that didn't mistake a single safe file for malware.

While Security Essentials excels at removing malware from a PC, it doesn't do as well at keeping dangerous code off a computer in the first place. It fully blocked 71.4 percent of new malware in our real-world tests, slightly worse than average. In our zoo test, it detected 97.0 percent of known malware samples. With that result, it lags the competition--some packages detected over 99.9 percent of samples.

Security Essentials didn't unduly slow overall system performance, but it performed a good deal worse than average in file-copy tests and app-installation tests. In scan speeds it also fell behind the pack: Its on-demand scanner completed our virtual obstacle course in a worse-than-average 3 minutes, 56 seconds. The on-access scanner was poky too, clocking in at 6 minutes, 43 seconds.

Although Microsoft Security Essentials has some good qualities, you would be better served by looking at some other options.