Denial of Service (DoS) attacks are important topics for security courses that teach ethical hacking techniques and intrusion detection. This paper presents a case study of the implementation of comprehensive offensive hands-on lab exercises about three common DoS attacks. The exercises teach students how to perform practically the DoS attacks in an isolated network laboratory environment. The paper discuses also some ethical and legal issues related to teaching ethical hacking, and then lists steps that schools and educators should take to improve the chances of having a successful and problem free information security programs.