Life has reached a stage where we cannot live without internet enabled technology. New devices and services are being invented continuously with the evolution of new technologies to improve our day-to-day lifestyle. At the same time, this opens many security vulnerabilities. There is a necessity for following proper security measures. Cybercrime may happen to any device/service at any time with worst ever consequences. In this study, an overview of the concept of cyber security has been presented. The paper first explains what cyber space and cyber security is. Then the costs and impact of cyber security are discussed. The causes of security vulnerabilities in an organization and the challenging factors of protecting an organization from cybercrimes are discussed in brief. Then a few common cyber-attacks and the ways to protect from them are specified. At last, a famous case study of Mirai’s attack on a few high-profile victims and the impact is presented.