For those wondering why, there was a
zero day exploit discovered some days ago that allows remote code execution (that's bad) using the Java applet plugin in your browser. Some sources suggest uninstalling Java, but don't do that--there's nothing wrong with Java and you need it for things like Minecraft. However, the browser plugin (like Flash) sucks, it's insecure, and no one uses applets much except for some ancient intranets.