The latest concern is the announcement of a new critical security flaw in Java SE 5 build 1.5.0_22-b03, Java SE 6 build 1.6.0_35-b10, and the latest Java SE 7 build 1.7.0_07-b10. This error is caused by a discrepancy with how the Java virtual machine handles defined data types (a type-safety error) and in doing so violates a fundamental security constraint in the Java runtime, allowing a complete bypass of the Java sandbox.
While this bug is more widespread than other recently found Java exploits, so far there is no concrete evidence of it being used in any malware exploits; however, it does stress the importance of reducing the number of active runtimes (code execution environments) on your system. If you do not need Java, then you might be best off uninstalling or disabling it. If you are unsure whether or not you need Java, then you might also remove it and then only reinstall it if any of your activities prompt you for a Java runtime requirement.