Login to your server as "root". Then type in the following:
Now type in the security login message you wish all users to see.
All activity is logged and regularly checked by systems personal. Individuals using this system without authority or in excess of their authority are subject to having all their services revoked. Any illegal services run by the user or attempts to take down this server or its services will be reported to local law enforcement, and said user will be punished to the full extent of the law.
Now type Ctrl+X then press Y and enter.
Logout of SSH then log back in, you will receive your new greeting.