Cloud computing gets its name from the drawings typically used to describe the Internet. It is a new consumption and delivery model for IT services. Cloud computing offers great potential to improve productivity and reduce costs, but at the same time it possesses many security risks. In this paper, the authors identify the possible security attacks on clouds including: denial of Service attack, Authentication attack Man-in-the Middle attack, Wrapping attacks, Malware-Injection attacks, Flooding attacks, Browser attacks, and also Accountability checking problems. They identify the root causes of these attacks and propose specific solutions.