Using Avira will by no means leave your PC completely open to malware, but you should consider the higher-scoring AVG, Avast, or Panda first.
Next: Microsoft Security Essentials, and more, plus supplementary tools.
Microsoft Security Essentials
Microsoft Security Essentials 2.1, our fifth-place finisher, 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% of the malware. It removed all traces of malware 80% 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% of new malware in our real-world tests, slightly worse than average. In our zoo test, it detected 97.0% of known malware samples. With that result, it lags the competition—some packages detected over 99.9% 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.
While Microsoft Security Essentials has some good qualities, you would be better served by looking at some other options.
PC Tools AntiVirus Free
PC Tools AntiVirus Free 2012 has its strong points, but it was the worst of the field when it came to blocking new malware. In our real-world blocking tests, PC Tools managed to stop only 57.1% of malware samples, placing it well behind its competition in this roundup.
On the plus side, PC Tools detected 99.96% of known malware from the past four months. It is also one of the best free antivirus programs at disinfecting a PC. It detected all infections on our test system, and it successfully disabled 93% of the infections. It removed all traces of malware in 73% of the cases.