Oracle has released a new Version 6 Update 22 of its Java software (which it acquired along with Sun Microsystems). This version fixes 29 identified security vulnerabilities; further details are in the Critical Patch Update Advisory, and in the Update Release Notes. A number of other bugs were also fixed.
The new version is available for Windows, Linux, and Solaris systems, and can be downloaded here; alternatively, the update mechanism included with the software can be used. (Mac users should note that Apple maintains its own versions of Java, and typically takes at least a few weeks to get the latest updates.) Because of its security content, I recommend installing this update as soon as you conveniently can.