Cloud computing is based on three principles which are distributed systems, grid computing and utility computing. It provides high performance infrastructure according usage of virtualization to offer capabilities such as on demand self-service, pay per use, highly scalable, rapid elasticity and huge amount of resource pools through the Internet. Everything in cloud environment is used as a service. Security is one of the most significant concerns in this environment such as confidentiality, integrity, availability, authenticity, and privacy. A lack of security in Infrastructure-as-a-Service (IaaS) as a fundamental delivery layer in cloud computing has an effective impact on the others delivery layers which are built on top of this layer.