Researchers from the Swiss Federal Institute of Technology looked at how many times over the past six years the two vendors were able to have a patch available on the day a vulnerability became publicly known, which they call the zero-day patch rate.

They analyzed 658 vulnerabilities affecting Microsoft products and 738 affecting Apple. They looked at only high- and medium-risk bugs, according to the classification used by the National Vulnerability Database, said Stefan Frei, one of the researchers involved in the study.

What they found is that, contrary to popular belief that Apple makes more secure products, Apple lags behind in patching.

"Apple was below 20 [unpatched vulnerabilities at disclosure] consistently before 2005," Frei said. "Since then, they are very often above. So if you have Apple and compare it to Microsoft, the number of unpatched vulnerabilities are higher at Apple."

It's generally good for vendors to have a software fix available when a vulnerability is disclosed, since hackers often try to find out where the problem is in order to write malicious software to hack a machine.

For a vendor to have a patch ready when the bug is detailed in public, it needs to get prior information from either its security analysts or external ones. Otherwise the vendor has to hurry to create a patch, but that process can be lengthy, given the rigorous testing needed to test the patch to ensure it does not conflict with other software.

Apple only started patching zero-day vulnerabilities in late 2003, Frei said.

"We think that Apple had fewer vulnerabilities early on, and they were just surprised or not as ready or not as attentive," Frei said. "It looks like Microsoft had good relationships earlier with the security community."

Over the past few years, Microsoft has tried to cultivate a closer relationship with the security community in order to encourage researchers to give it a heads-up about software problems. Apple, however, doesn't appear to have that same sort of engagement yet, and, "based on our findings, this is hurting them," Frei said.

Curiously, both vendors' abilities to have zero-day patches ready at disclosure seemed to dip in the six months before a major product release. That trend was most pronounced in 2004 and 2005. Frei theorized that the buildup to big software releases took away software engineering resources.

Andrew Cushman, director of Microsoft's Security and Research, said he couldn't pinpoint what might cause that trend. But in 2004 and 2005, Microsoft had a rash of vulnerabilities pop up in its Office products that it did not get advance notice of, which may have contributed to a higher percentage of unpatched publicly disclosed bugs.

However, the study proved to be such a glowing affirmation of Microsoft's increased focus on security in the past few years that it prompted Cushman to ask Frei, "Did Microsoft fund this research?"