"And the answer is... Microsoft. Researchers from the Swiss Federal Institute of Technology analyzed 658 high-risk and medium-risk vulnerabilities affecting Microsoft products and 738 affecting Apple. They measured 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 0-day patch rate. What they found: 'Apple was below 20 [unpatched vulnerabilities at disclosure] consistently before 2005,' said Stefan Frei, one of the researchers involved in the study.