A Java patch released recently is reported to fix at least 19 security vulnerabilities. Ten of those vulnerabilities are rated as severe.
Java is used in a wide range of web-based applications. While its safety has increased lately, it is thought to be because hackers are going after other programs like Microsoft's Silverlight. Still, because it is widely used and is relatively porous with security holes, it's recommended that if you don't specifically need Java that you uninstall it, just to be safe. Otherwise, as with any prgram or application, make sure you keep it as up to date as possible.
You can download Java here, although Java has reported there will be an automatic updater in the future. Still, it's best to go ahead and fix it now instead of waiting and risking a hack.