The Additional Message on Login Parameter
The option to display an additional message on login to a Windows Client computer allows you to inform the user that their actions are being monitored, and also to notify them of corporate policies or the laws of the country, as well as obtain their consent to be monitored.
If the Enable displaying of additional message checkbox is selected (on the Editing Client / Editing Client Group page, on the Authentication Options tab, in the Authentication Options section at the top) to enable this option, the Client will display an additional pop-up message window to the user on login to the Windows Client, and after (reading the message displayed, and providing their consent if required, and) clicking the Continue button, will they be allowed to access the system.
For more information, see Enabling the Displaying of an Additional Message on Login to Windows Clients.