Due to multiple and in-use vulnerabilities that are actively affecting user systems, Apple has taken the step of blocking the web plug-ins for all older versions of Java 6 and 7. Browsers on Snow Leopard, Lion and Mountain Lion that don't include their own built-in versions of the Java plug-in must be updated to the current version, which is update 17 for Java SE 7 and update 43 for Java SE 6. Java is not installed on modern Macs by default, and disabled automatically if not used for 31 days or more even if installed. The move does not affect local installations of Java, only the web plug-in.
