A data center is a fixed environment where applications run on dedicated servers that can only be accessed by authorized users. In contrast, a cloud environment is dynamic and automated, where pools of computing resources are available to support application workloads that can be accessed anywhere, anytime, from any device. For the experienced information security professional, it seems that many of the principles that make cloud computing attractive run counter to network security best practices. What follows are the top three considerations for securing traditional and cloud-based data centers, as well as key requirements for cloud security.