What is the necessary action to safeguard on-premises computers using Microsoft Defender installed in an Azure subscription?

To safeguard on-premises computers using Microsoft Defender in an Azure subscription, installing the Connected Machine agent is necessary. This agent enables the integration of on-premises machines with Azure, allowing them to be managed and monitored through Microsoft Defender for Cloud.

When the Connected Machine agent is installed on an on-premises computer, it facilitates the linking of that machine to Azure, thereby enabling security policies to be applied and providing visibility, threat detection, and other security features directly from the Microsoft Defender platform. This ensures that on-premises resources receive the same level of protection and monitoring that cloud resources do.

While the other options mention agents and roles that play significant parts in Azure management and monitoring, they are not specifically aimed at securing on-premises machines. The Log Analytics agent, for instance, is used for collecting data for monitoring and logging purposes rather than securing machines. The Hybrid Runbook Worker role is intended for executing runbooks that manage hybrid workflows. The Dependency agent is used for application mapping and managing dependencies rather than providing security.

Thus, installing the Connected Machine agent directly supports the integration required to safeguard on-premises computers effectively within the Microsoft Defender ecosystem.