On Wednesday, AV-Test failed Microsoft Security Essentials in its antivirus certification program, claiming that Microsoft's program only protected against 78 percent of "day 0" malware attacks. It also claimed that it detected 90 percent of the malware that has come up in the last few months, when the industry average is 97 percent.

Microsoft has since give their own statement on AV-Test's findings. As far as the "day 0" statistics, Microsoft says, "We know from telemetry from hundreds of millions of systems around the world that 99.997 percent of our customers hit with any 0-day did not encounter the malware samples tested in this test." In addition, Microsoft said that 94 percent of the malware that AV-Test says Microsoft Security Essentials missed "were never encountered by any of our customers.'

Microsoft says that it is working to cut down "our 0.0033 percent margin to zero." It added:

In December 2012, we processed 20 million new potentially malicious files, and, using telemetry and customer impact to prioritize those files, added protection that blocked 4 million different malicious files on nearly 3 million computers. Those 4 million files could have been customer-impacting if we had not prioritized them appropriately.

Source: Microsoft Malware Protection Center blog | Image via Microsoft