This document discusses security issues in cloud computing. It begins by defining cloud computing and describing its service models and deployment models. It then identifies several key security issues in cloud computing, including security, privacy, reliability, lack of open standards, compliance, and concerns about long-term viability of data. Security is identified as the top challenge according to a survey of IT executives. The document argues that more must be done to address security, privacy, and other issues in order to fully realize the potential of cloud computing.