The number of patches -- nearly two dozen -- is higher than usual for an odd-numbered month; for some time, Microsoft has used an even-odd schedule, patching more vulnerabilities in the even months, when it also regularly updates Internet Explorer.

"May has been a light month, historically, very light," said Andrew Storms, director of security operations at nCircle Security, who tracks the number of patches and updates Microsoft issues each month.

In May 2011, Microsoft shipped two update that . The year before, it delivered two updates that patched two bugs.

"So, this is a big number," said Storms.

The pace so far this year -- Microsoft's collections during the first five months have included seven, nine, six, six and seven updates -- puts to rest the idea that Microsoft still hews to a wave-and-trough practice.