This study analyzes the security of the OS X operating system. Through the historical development of OS X are presented security features that were introduced with each version. I touched the transition from Mac OS Classic, trough NeXSTEP to modern OS X systems. Architecture of OS X is explained in an understandable and picturesque way. Throughout the chapter the basics of security I detailed important security mechanisms of the system. In the same chapter are explained the user security features that provide security of user data and easy control of safety for the end user. Testing the security of a particular system is achieved in stages, and there is an explanation of each phase. There is an explanation of the importance of each phase, completed actions and software tools used in each phase. Vulnerability assessment of system was carried out using a Nessus tool on OS X version Mavericks, and was conducted in two parts. The first part is explained and illustrated conduct of vulnerability assessments, while the second part analyzes the results and explains safety recommendations to address found systemic vulnerabilities. Vulnerability testing has purpose to confirm the possibility of exploiting vulnerabilities found with vulnerability assessment. To carry out the vulnerability testing we used famous Metasploit tool that contains a number of functionalities to exploit found vulnerabilities in system. In the last chapter we provide a description of the tools Nessus and Metasploit, which we used to test the security of the OS X system. It describes their creation and development, the main components, how they work and theirs role in today's world of computer security.