Researchers at the independent anti-virus testing firm AV-TEST released their latest batch of tests in which they report Microsoft Security Essentials was only able to detect 64% of zero-day threats when running in Windows 7.

Due to the pitifully low score, MSE failed to receive the AV-TEST Institute’s seal of approval, a certification granted to products that meet 11 of 18 assessment criteria. Those criteria consider the effectiveness of software at detecting and blocking threats, repairing infected systems and overall usability including “average slowing down of the computer when the software is used on a daily basis, false positives during a system scan and the display of false warnings or the blocking of certain actions during the installation and during the use of known good software.”

During the month of October, AV-TEST rated Security Essentials versions 4.0 and 4.1 at just 1.5 out of 6 in terms of its PC protection, thanks largely to the 64% zero-day detection rate that’s well below the industry average of 89%. MSE is the only product of 24 for Windows 7 that has not received the AV-TEST certification. Six other AV products also did not receive the certification for Windows Vistaor for Windows XP. Anti-virus software for Windows 8 has yet to be tested and Microsoft is absent from AV-TEST’s list of vendors thanks to the new OS’ integrated protection software.

FYI, Microsoft Security Essentials has lost AV-TEST’s seal before, with its test failing to meet the lab’s standards. The AV-TEST Institute conducts tests on a bi-monthly basis and usually finds that Microsoft Security Essentials consistently struggles to perform well in its malware detection and blocking tests.

Final thoughts:

Free antivirus software usually provides only a bare minimum level of protection.

If you currently use MSE (or another free product) and are having trouble keeping your machines clean, it might be time to invest in a more robust and complete anti-virus software solution.