Apple has released a security update for the Apple-supported Java runtime for OS X, which many users have installed on their systems. Java for OS X is available for Apple's latest three OS X releases starting with Snow Leopard. The update should be available through Apple's Software Update service (in the Apple menu).
This update was released by Oracle last week to tackle a few outstanding vulnerabilities (separate from those recently found in its latest Java 7 runtime), but since Java 6 for OS X is maintained and distributed by Apple, OS X users have had to wait until Apple issued the update.
Apple has released one updater for OS X 10.6 and one for OS X 10.7 or later that will bring the Java 6 runtime installation in OS X systems up to the latest version, version 1.6_35.
If you use Software Update to update your system then you do not need to select individual packages to use, but if you download them manually then be sure to use the one that is appropriate for your operating system:
Since this update addresses a known security vulnerability that could be exploited, if you have Java installed on your system then be sure to update it. If you are uncertain whether or not you have Java installed, then run Software Update and if you see this update as being available then download and install it.