Nowadays Cloud computing, as one of the focus point in IT world, it has drawn great attention. Many big IT companies like IBM, Google, Amazon, Microsoft, Yahoo develop cloud computing systems and related products to customers. However, there are still many difficulties for customers to adopt cloud computing, in which manly many security issues exist, because data of a customer is stored and processed in cloud, not in a local machine. This paper I will briefly introduces cloud computing and its key concepts. Specially, we aim to discuss security requirements and security issues in cloud computing. We will discuss security issues in data and virtualization in cloud computing
