The message can be ignored, or can it? http://technet.microsoft.com/en-gb/library/hh344223.aspx. It only states since if you use an account in local admin group it gives that account the right to execute malicious codes without even prompting to execute.

Add the farm account into the local administrators group. This is stated in the TechNet article:http://technet.microsoft.com/en-us/library/ee721049.aspx

"The Server Farm account, which is created during the SharePoint farm setup, must also be a member of the Administrators group on the server where the User Profile Synchronization service is deployed."

There seems to be some conflicting opinions about the correct permissions, as this will cause the SharePoint Health Analyzer to create a warning:

"Accounts used by application pools or service identities are in the local machine Administrators group. Using highly-privileged accounts as application pool or as service identities poses a security risk to the farm, and could allow malicious code to execute."

Also grant the Replicate Directory Changes [http://support.microsoft.com/kb/303972] permission for the farm account. Reboot the server to make sure that all the services using the farm account run with the new privileges.

Make this a point for site app pools:
As a SharePoint best practice, please refrain from using built-in machine administrator account for any SharePoint site app pools (services, application pools).

From the article on technet: http://technet.microsoft.com/en-us/library/cc678863(office.12).aspx (though the article is for MOSS 2007, it is still relevant)

The other application pool account must be a domain user account. This account must not be a member of the administrators group on any computer in the server farm.