When the attack applet is executed, it can read, modify, or destroy any data on the computer, insert a virus, insert software to spy on the user's future online activities, or take any other malicious action. The attack does not require the user to do anything beyond viewing the Web page or e-mail message, according to the Princeton group. The flaw is a programming error in one of the security-critical parts of Microsoft's Java class libraries. A malicious applet can exploit this error to violate Java's security rules, known as the Java Sandbox. The bug affects only Microsoft's JVM, as the coding is different for other companies' JVM technology, he added.
Different vendors have different code.
So far the only people who have been finding these major holes in Java happen to be good guys. However, the very nature of how hackers would make use of the bug to gain access to systems would behoove them to keep quiet about it, according to Mobile code security vendor Finjan. The patching model is great for Microsoft to turn around and say we've got a fix for the problem. But until that is actually deployed in large organizations, there is always going to be some machines that are going to be vulnerable.