Avast! WebShield will block these exploits. They are usually designed to exploit a vulnerability in the MS Java Virtual Machine, as a previous posting mentioned. On a vulnerable machine, they will download a Trojan horse, and spyware like CoolWWWSearch.
Java code runs in a sandbox, as is not able to execute malicious actions outside of that sandbox. As long as the sandbox has no 'holes' it is safe to run Java code. The key to running Java safely is therefore to check regularly for updates to the Java plug-in to ensure that any 'holes' or security vulnerabilities are patched.
The MS Java plug-in is obsolete and should be shown the door.
The Sun Java Plug-in has also had vulnerabilities. Make sure you have the latest version: 1.5.0_3.
http://java.sun.com/j2se/1.5.0/download.jspDelete these files by clearing the Java cache.
http://www.java.com/en/download/help/cache_virus.xml