closed as not constructive by daviesgeek, patrix♦, Stu Wilson, jmlumpkin, Mark Sep 24 '12 at 12:34
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As a security person, here is what I recommend:
This kind of question is not Safari-specific. For those kinds of non-Apple-specific questions, Security.SE is another good resource.
Java is a general purpose programming language and associated runtime originally developed by Sun. Java programs can run inside a browser plug-in. There have been some recent vulnerabilities uncovered, and Apple has taken the step of disabling Java by default.