A great opportunity for all those cracks out there. As part of the development of Mustang (Java 1.6), Sun is developing a new, smaller and faster classfile verifier which they want your help in trying to break.
According to VP Graham Hamilton puts - As part of Mustang we will be delivering a whole new classfile verifier implementation based on an entirely new verification approach. The classfile verifier is the very heart of the whole Java sandbox model, so replacing both the implementation and the basic verification model is a Really Big Deal. The new verifier is faster and smaller than the classic verifier, but at the same time it doesn't have the ten years of reassuring shakedown history that we have with the classic verifier.
You can join the new Crack the Verifier initiative to if you think you can break it. So go and get your hands wet.