Mainframe is a game mode available only in custom games. It adds three extra roles to the game: Admin, Nuker, and Scripty.
The admin knows who all of the hackers are from the start of the round. The nuker is just a hacker, but at the end of the match, if three nodes are secured, they will get the power to 'nuke' one of the agents. If the nuker nukes the admin, the hackers will win. The scripty is only available in games with 7-8 people. The scripty does not know who the other two hackers are. The other two hackers also do not know who the scripty is. However, the admin will know all three of the hackers.
As the admin, you want to communicate with your agent team who the hackers are, while keeping your role as admin secret from the hackers.