The subject that is covered on this paper is ethical hacking in scope of IT security. Through this paper you will be informed about the terms hacking, the difference between hackers and ethical hackers and how we categorize them. With their knowledge and skills they do penetration testing through defined phases of the process so they would get the information on what are the vulnerabilites and exploits of targeted system and how it can be mitigated . In this paper the process of testing and it's phases are described, rules and standards as well as all the methods, techniques and tools they are using. In addition, we address the financial benefit to hackers and describe the collaboration with security companies in enhancing IT security through bug bounty programs. It will also be shown how, with the use of certain programs and tools, you can get to very valuable information about your target. Moreover, the target for pentesting in this paper was web server vulnerability testing with the use of Nmap. Testing was done on legal sites designed for this kind of testing.