GDM includes a graphical application that you can use to configure GDM. The following steps document how to disable remote login with this application:
To disable remote login
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Run /usr/bin/gdmsetup. 
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Click the XDMCP tab. 
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Verify that the Enabled XDMCP is not selected. 
NOTE: Whether modifying the GDM configuration manually or by using /usr/bin/gdmsetup, you must restart GDM.
