What is the best way to ensure that only approved users and domain groups have membership in the local Administrators group on each desktop?

Define a Policy: The first step is to define a policy that only approved users and domain groups should have membership in the local Administrators group. This policy should be communicated to all relevant parties.

Use Group Policy: You can use Group Policy to manage local group membership. This can be done by creating a Group Policy Object (GPO) and linking it to the appropriate Organizational Unit (OU) that contains the desktops.

Configure Restricted Groups: Within the GPO, you can configure Restricted Groups. This allows you to specify which users or groups should be members of the local Administrators group.

Apply the GPO: Once the GPO is configured, it needs to be applied. This can be done by running the "gpupdate /force" command on the desktops or by waiting for the Group Policy refresh interval.

Regular Auditing: Regular audits should be conducted to ensure that the policy is being adhered to. This can be done manually or by using tools that can automate the process.

Remediation: If any unauthorized users or groups are found during the audit, they should be removed from the local Administrators group and the incident should be investigated to prevent future occurrences.

Training and Awareness: Regular training and awareness sessions should be conducted to ensure that all users are aware of the policy and the importance of adhering to it.