Malwarebytes Antimalware Free 1.61 is a supplemental free product that can help bolster your existing security software. The makers of Malwarebytes Antimalware pitch it as a tool for detecting and removing brand-new "zero-day" malware, and it uses a number of different technologies to accomplish this task.

The software did perform decently compared with other freebies in PCWorld's 2012 free antivirus roundup when it came to stopping new malware. In our real-world tests, Malwarebytes fully blocked 78.6 percent of samples--slightly better than average--and partially blocked an additional 14.3 percent. It's also reasonably fast: It had the lightest overall impact on system performance of any free antivirus product we tested.

Malwarebytes isn't something you'll want to use as your primary antivirus software, though, as it isn't great at stopping known malware: It detected a scant 57.1 percent of known malware samples collected from the past four months--far and away the worst result we saw from any of the freebies tested.

The software has a fairly no-frills interface, but it's straightforward. One clever feature is Chameleon, which lets the program run even when a particularly evil piece of malware attempts to block it.

Malwarebytes' makers don't see its product as a front-line antivirus de­­fense, and frankly, neither should you. But it's something to consider adding to your security toolbox.