Public, private, and hybrid clouds have different characteristics in terms of technology leverage and ownership, management of provisioned resources, workload distribution methods, security and data privacy enforcement, and example platforms. Infrastructure as a service (IaaS), platform as a service (PaaS), and software as a service (SaaS) are the three main service models for cloud computing, with each offering a different level of service and control over the infrastructure. Ensuring security across these cloud service models presents challenges that providers aim to address through techniques like trust overlays, data watermarking, and access control measures.