In this paper, the authors discuss the cloud security issues. Cloud computing is a "Network of network" over the internet, therefore, chances of intrusion is more with the erudition of intrusion attack. Cloud system security is one of the most important issues that have attracted a lot of research and development effort in past few years. Particularly, attackers can explore vulnerabilities of a cloud system and compromise virtual machine to deploy further large-scale Distributed Denial Of Service (DDOS). An intrusion detection system is used to detect several types of malicious behaviors that can compromise the security and trust of computer system.