Remove java from Control panel–> program.
Then go here , http://java.com/zh_CN/download/installed.jsp
click on “Verify Java”.

If it ask to down load Java, or to run a disabled plug-in, then it means this PC is safe.

About why:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2012-4681