Cloud computing is an evolving paradigm with tremendous momentum, but its unique aspects are exacerbating security and privacy challenges. However, when it comes to security, Cloud providers and customers must share the responsibility for security and privacy in cloud computing environments, but sharing levels will differ for different delivery models, which in turn affect cloud extensibility:
In SaaS
The providers typically enable services with a large number of integrated features, resulting in less extensibility for customers. Providers are more responsible for the security and privacy of application services, more so in public than private clouds where the client organization might have stringent security requirements and provide the needed enforcement services. Private clouds could also demand more extensibility to accommodate customized requirements.