Microsoft Security Essentials 2.1, the fifth-place finisher in PCWorld's 2012 free antivirus roundup, is something of a mixed bag. I like its interface, and it is reasonably good at cleaning up infections, but it falters at stopping new malware, and it plods through its chores.

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.

--Nick Mediati