Sometimes, errors are obvious and exploits are easy. Other times, experimentation is required to turn a potential flaw into a real exploit. All of the holes described in this chapter can be exploited using attack applets. That means the holes covered here are not esoteric flaws that are impossible to exploit. Every Java hole described in this chapter has an accompanying exploit.
Holes are just vulnerabilities.
Sometimes a hole will be recognized as a hole but cannot be exploited by itself. In these cases, multiple holes together create an exploit. Think of attacking a system as climbing up a cliff. When you reach the top, you have successfully completed an attack. A security hole can be likened to a piton in the cliff with a piece of rope attached.