One of the recent security holes that Apple dug itself into recently was the mishap that resulted from its lack of attention to the Java runtime for OS X, whereby leaving it unpatched for over a month allowed the Flashback malware to take advantage of many OS X systems. Since this incident, Apple appears to be paying more attention to security updates for its supported Java runtime.
Today Oracle released a new version of the Java runtime, and while in the past Apple has lagged a number of weeks behind Oracle's releases, the company was hot on the heels of the Java release and issued its own update very shortly after Oracle's.
The Java update for OS X is available for anyone who has Java SE 6 installed on Snow Leopard or Lion, and should be available through Software Update, but can also be downloaded from the following locations (note that if you do not see these updates available in Software Update, then you likely do not have Java installed and do not need to install them manually):
As always, be sure to back up your system before installing these or any other updates.