The update, released early Tuesday afternoon, Pacific time, fixes 13 bugs in various OS X components, including core components such as Apple Type Services and CFNetwork. It's Apple's fifth OS X security update this year.
Many open-source OS X components are also patched, including Samba, PHP and ClamAV software.
At least six of the bugs theoretically could be exploited by attackers to run unauthorised software on the Mac, Apple said.
Microsoft's Windows operating system remains the favorite target of online attackers, but security experts say it's always a good idea to install these security updates as quickly as possible, no matter what the product.