Explanation:

IaaS (Infrastructure as a Service) provides the least built-in security because it mainly offers virtualized computing resources over the internet (like servers, storage, and networking). Security responsibilities lie more with the customer who must secure OS, applications, and data.

PaaS (Platform as a Service) provides more built-in security than IaaS by handling OS-level security, runtime, and platform patches.

SaaS (Software as a Service) offers the most built-in security, as the service provider handles almost everything: application, data, runtime, middleware, OS, virtualization, servers, storage, and networking.

Final Answer: (C) IaaS ✅