Agent-based scanning is the correct approach as agents are installed directly on the target systems, allowing for continuous and real-time scanning regardless of the systems' network availability or configuration changes. Unlike agentless scanning, which requires network connectivity and can miss changes if the system is offline during the scheduled scan, agent-based scanning is more suitable for dynamic environments with remote or intermittently connected assets.

Using credentials is incorrect because, although it deepens the level of scanning, it doesn't address the concern of systems being offline. Scheduling frequent scans may fail to recognize changes made between scans for systems that change configuration rapidly and are not always online. Cloud-based assessment tools address different needs and are particularly designed for assessing cloud service configurations.