IaaS (Infrastructure as a Service), which is like if you rent a building you lock the doors, you control security and operations, and your responsibility is data security and firewalls. You’re responsible for securing everything. PaaS (Platform as a Service) is like when you own a kitchen (like a restaurant), you cook. So the provider manage servers and you control user access. SaaS (Software as a Service) is fully staffing your restaurant. The provider manage applications and infrastructure and you manage access permissions.

As you go from IaaS to Saas, a cloud provider take on security responsibility so customer takes on less.

Cornell University Information Technologies. What Does Cloud Have to Do with SaaS, PaaS, and IaaS? Cornell University, https://it.cornell.edu/cornell-cloud/what-does-cloud-have-do-saas-paas-iaas.

I think the Morris Worm incident allowed the CIA Triad to flourish because it exposed the problem the attack caused. Confidentiality was a concern as access grew. Integrity was threatened if systems didn’t behave properly and Availability was disrupted when it went down for several days.