What is the difference between a threat and an attack?  How do exploits relate to vulnerabilities?  Is there an ethically acceptable reason to study and use the various attack methods described in this module?

A threat can be defined as an interpretation or words that convey a vulnerability and a plan to act on it. An attack is an actual attempt to exploit that vulnerability. A threat can be defined as a risk of action that an event may occur. 

Exploits are ways vulnerability can be exposed. A vulnerability is a weakness or flaw and exploiting that is to use that flaw to gain access.

The study of various attack methods used is ethical as the primary job is to defend. Just like in a battle learning the other opponent’s tactics and predicting how they can be used. Learning methods others can attack and preparing ways to defend against such an attack is needed otherwise you will not know the best way to prevent or stop it. Using these methods for no reason I believe would be unethical, but to prevent an attack or catastrophe is just getting ahead as you are preparing. Another example is studying for a test. If you do not study you have no way to prepare for the exam and you are not sure what you will face