Apple has released Java for OS X 2013-004 and Java for Mac OS X v10.6 Update 16, which fix multiple vulnerabilities, the most serious of which may allow untrusted Java applets to execute arbitrary code outside the Java sandbox. (These updates bring Java to version 1.6.0_51.)
If you have Java 6 installed on your Mac (it is not installed by default in Mac OS X 10.8, Mountain Lion, or Mac OS X 10.7, Lion), you should install this update as soon as possible, as Java has become a popular method of exploiting a computer.
Java for OS X 2013-004 is available for Mac OS X v10.8, Mac OS X Server v10.8, Mac OS X v10.7 and Mac OS X Server v10.7. Java for Mac OS X v10.6 Update 16 is available for Mac OS X v10.6 and Mac OS X Server v10.6. For more information, see http://support.apple.com/kb/HT5797