The people at AV vendor Panda Software must have been quite busy. They audited 1.5 million home PCs and 1200 corporate networks looking for traces of infection.

They found that on the home PCs front, only around 37% were protected by an up-to-date protection (antivirus or antispyware). And among those, almost 23% were still infected by malware that should have been detected. "Infection", here,  means that an active malicious process was loaded in memory.

The corporate world is even less fortunate with about 72% of tested networks comprising of more than 100 workstations being infected. On those network, "infected" means that an active malware was trying to spread over the company LAN.

Viruses infecting protected PCs is not that new. Security pros have been observing it for years. It may come from human error, or product defect, either within the AV itself or with a specific signature file or a specific malware. We have seen during past live antivirus testing a known malicious code infecting a system right under the nose of products like Symantec or Panda. 

More recently, though, malware has been seen trying harder to defeat those protections. If not by wit (probably a lost Art with malicious code today), it's by sheer speed : malware-planting websites have been seen pumping new versions of their pest every couple hours to avoid detection.

Thus this study, while not breaking new grounds, provides some interesting figures about a well-known phenomenon. But we do need to be careful with those results : behind the study, Panda is trying to push it's TruePrevent HIPS solution and Collective Intelligence service. While those may not be bad products by themselves, and while the behavorial and collective "cloud" approach is not bad in itself, there is a marketing intend here. Besides, the metric for this study was a tool said to be specifically developed by Panda to detect unknown malwares. We can't rule out false positives from it, as from any other tool. 

A study like this one is only as good as its reference point, and in this study, nothing is known about it. Nevertheless, it confirms an interesting trend.