Hands-on experiments are essential for computer network security education. Existing laboratory solutions usually require significant effort to build, configure, and maintain and often do not support reconfigurability, flexibility, and scalability. This paper presents a cloud-based virtual laboratory education platform called V-Lab that provides a contained experimental environment for hands-on experiments using virtualization technologies (such as Xen or KVM Cloud Platform) and OpenFlow switches. The system can be securely accessed through OpenVPN, and students can remotely control the virtual machines (VMs) and perform the experimental tasks. The V-Lab platform also offers an interactive Web GUI for resource management and a social site for knowledge sharing and contribution. By using a flexible and configurable design, V-Lab integrates pedagogical models into curriculum design and provides a progressive learning path with a series of experiments for network security education. Since summer 2011, V-Lab has served more than 1000 students from six courses across over 20 experiments. The evaluation demonstrates that the platform and curriculum have produced excellent results and helped students understand and build up computer security knowledge to solve real-world problems.