Comodo Internet Security Premium came in fifth in our late 2010 roundup of free antivirus products. Although it was last among the products we tested, it did a very good job at blocking brand-new malware. Its detection of known malware lagged behind top performers, though, and it tied for the most false positives.

Comodo Internet Security is reasonably well designed and easy to use. Its installer takes several more steps than is becoming the norm for antivirus software, but it was perfectly usable otherwise. Once it's installed, you'll be greeted by a well laid out Summary screen that uses the familiar green/yellow/red status indicators for your PC's protection status, although some of the wording could have been better. The scan window, however, doesn’t give any indication as to its status--no progress bar, nothing--so you'll be somewhat in the dark as to how long you'll have to wait for scans to complete.

Unlike many free products, Comodo Internet Security has a firewall--thus the product's "Internet Security" moniker. We didn't test the effectiveness of the firewall, however.

Internet Security Premium's malware detection and blocking is a mixed bag. Its 92.4 percent detection rate in traditional scanner-based detection tests--which indicate how well a product can identify known malware--was the lowest score of any product we looked at. In addition, Comodo missed several samples in what's known as the WildList test. This test by itself isn't a good measure of an antivirus product's effectiveness--we don't include it in our scoring for this reason--but any security product worth its salt should be able to detect all its samples.

It also did a middling job at cleaning up infections on a test PC: It detected all test infections, and removed active components of malware infections 60 percent of the time, in a tie for the lowest score among the free antivirus products we reviewed. That said, no product we looked at achieved higher than an 80 percent removal rate.

False positives was another concern: Internet Security Premium tied with Avira AntiVir Personal for the most false positives (six) in traditional malware detection, and it was the only product among the antivirus packages we tested to flag safe files as possibly malicious in dynamic malware detection tests (dynamic malware detection technology attempts to identify malware based solely on how it behaves--a good way of identifying brand-new malware for which no signature file exists). While as a percentage, the number of false positives is low, even one false positive can cause problems.

Despite this issue, Comodo Internet Security Premium did an excellent job at blocking brand-new malware. In tests for blocking real, live malware, Comodo completely blocked 96 percent of attacks, and partially blocked the other 4 percent. No other product was able to fully block more than 80 percent of new malware attacks.

Scan speeds were a mixed bag as well. Its on-demand scan speed (how long it takes to scan 4.5GB of data for malware in an manually initiated scan) of 2 minutes, 9 seconds was solid, though it trailed the fastest scan time of 87 seconds. An on-access scan of 4.5GB of data took 5 minutes, 4 seconds, which was slightly longer than the average. The on-access scan test determines how quickly a product can scan files as they're opened or saved to disk.

In other speed tests, Comodo Internet Security Premium had a relatively slight impact on PC performance. It added less than 1 second to startup times when compared to a PC with no antivirus software installed, though some file copy and download tests took longer than the average for the products we tested.

Comodo Internet Security Premium is by no means a bad product, but its mixed detection scores make it hard to recommend. It may be worth considering on the strength of its detection of brand new malware, but you can find security products that are more well rounded.