Cloud computing has emerged from the legacy system; consequently, threats applicable in legacy system are equally applicable to cloud computing. In addition, cloud specific new threats have also emerged due to the various reasons including, multi-tenancy, access from anywhere, control of cloud, etc. Considering the significance of cloud security, this work is an attempt to identify the major threat factors to cloud security that may be critical in cloud environment. It also highlights the various methods employed by the attackers to cause the damage. To accomplish our objective, we have reviewed the major publication related to cyber security. It is revealed that cyber-attacks are industry specific and vary significantly from one industry type to another. Finally, we have conducted the case study on cyber-attacks that are already occurred in cloud paradigm. Cyber-attacks were highlighted by categorizing them into phishing attacks and distributed denial of services. This work will be profoundly helpful to the industry and researchers in understanding the various cloud specific cyber-attack and enable them to evolve the strategy to counter them more effectively.