Apple has blocked the Java plugin on OS X after a vulnerability was discovered. The Oracle software is on the blacklist and will probably only be unlocked if the vulnerability is resolved by Oracle.
MacRumors discovered a reference to the blockade of the Java plugin found in the Xprotect.plist file. It is a Java version required that does not exist, thus effectively existing Java plugins are being blocked. Apple introduced the blockade through an update of the Xprotect.plist file, something that works for users of Mac OS X version 10.6 and higher. In older version you will have to uninstall it manually.
Following the discovery of the vulnerability in Java, the U.S. government advised not to use Java more. The public authority Cert encouraged users to turn plugins off in their browsers off.