Apple's latest Java update requires you periodically enable the Java plug-in manually. Here is how this works in OS X.

Although Java initially was hailed in the mid-1990s as a way to run client-side applets, the platform instead became known for its server-side capabilities.

If you do need it, unplug it from the browser unless and until you need it. Java 7 lets users disable Java content in web browsers through the Java control panel applet.