The blockage, which was announced internally to AppleCare and Apple Retail employees, is because of an "unspecified vulnerability" and Apple has blocked Java 6 versions below update 51, and Java 7 versions below update 25.
At the beginning of this year, Apple blocked Java plug-ins in Safari several times because of unfixed vulnerabilities. Oracle has typically updated Java fairly quickly to remedy the vulnerabilities.
Users are strongly advised to ensure they have the latest versions of Java.
Article Link: Apple Again Blocks Older Versions of Java Over Vulnerability