Security Update 2008-008, which was released Monday as part of a broader refresh of Mac OS X 10.5, aka "Leopard," and available separately for users of Mac OS X 10.4, also known as "Tiger," quashes bugs in Apple Type Services, the CoreGraphics rendering component, Kernel, LibSystem and other pieces of the operating system.

At least half a dozen of the patches were tagged by Apple with its usual "arbitrary code execution" phrasing, a sign that the vulnerabilities are serious and, if exploited, could result in a hacker hijacking the machine.

While all 21 of the vulnerabilities affect Leopard, which was updated to version 10.5.6, only 15 of them affect Tiger, Apple's oldest still-supported OS.

Apple also updated the Flash Player plug-in it ships with Mac OS X to bring the software in line with the versions and Nov. 17. Although Adobe updated Flash for all users, Mac included, and made the new versions available for downloading, Apple includes the fixes in its own operating system updates because it bundles the plug-in with all its computers.

"The issues are addressed by updating the Flash Player plug-in to version 9.0.151.0," said Apple in the that accompanied Monday's patches. These fixes will be moot for users who have already updated to Flash Player 10 on their own, however.