Updating pre-login security warning

A system I have inherited sends a message to users to warn that use of the system is for Official Business only… and warning of penalties for unauthorized use.. This message is sent to the users before they are prompted for their username.. and before the /etc/issue file is output. I need to update the contents of the message but I can’t find the mechanism that is sending it..

Can you offer a suggestion as to where I might look for the message text?