Final answer:
The Azure Policy action to deploy Microsoft Antimalware on VMs where it isn't installed is DeployIfNotExists. It checks for the condition and deploys the remediation if necessary. This action can be set up in the Azure portal or through Azure Resource Manager templates.
Step-by-step explanation:
The Azure Policy action that allows you to deploy Microsoft Antimalware on virtual machines where it is not currently installed is called DeployIfNotExists. This action evaluates resources for a specified condition and deploys the defined remediation if that condition is not met. For example, if the policy is set to ensure that all virtual machines have Microsoft Antimalware installed, the DeployIfNotExists action will automatically deploy Microsoft Antimalware to VMs without it. Policies can be created within the Azure Policy service in the Azure portal or using Azure Resource Manager templates.