This document discusses security issues related to cloud computing. It begins with an introduction to cloud computing models including Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). It then discusses potential security attacks to clouds like denial of service attacks and man-in-the-middle attacks. Security concerns with moving data and applications to the cloud are outlined. Techniques for securely publishing data in the cloud are also presented. The document concludes that security in cloud computing is challenging due to the complexity of clouds but that assurance of secure and mission-critical operations is important.