A JRE exploit has reportedly hit the wild. Context here.  Some kind Redditor has posted instructions on disabling the JRE in various browsers:

• In Firefox : Press Firefox button -> Add-ons, go to Plugins and click the “Disable” button next to anything named “Java”.
• In Chrome : Type in: “chrome://plugins/” into the address bar (no quotes). Scroll down to Java and click disable.
• In Opera: Type in “opera:plugins” into the address bar (no quotes). Scroll down to:
  • Java(TM) Platform <click on> Disable.
  • Java Deployment Toolkit <click on> Disable.
• In Internet Explorer:
  • Disable UAC (if enabled) and restart.
  • Open the Java app in Control Panel.
  • Go to advanced tab.
  • Expand Default Java for browsers.
  • The checkbox next to IE is grayed out.  Select Microsoft Internet Explorer and press spacebar. Click OK.
  • You can re-enable UAC and restart now.