Cloud computing is an emerging technology which provides services on the basis of as the users' pay-as-you-go. It provides resources (e.g. CPU and storage) as general utilities that can be leased and released by users through the internet in an on-demand fashion. But deploying cloud computing in an enterprise infrastructure brings significant security concerns. Though cloud computing have an economical computation over the current infrastructure but implementation of cloud computing in an enterprise requires proper planning and understanding of emerging risks, threats, vulnerabilities and possible countermeasures.