The message of the day (motd) file is used by the System Administrators to display information to users when the log in to a system using a command line tool (for instance ssh). On older systems, it was a single text file located in /etc/motd. On Ubuntu, after around v10.10, it was changed to a series of scripts that are executed instead of simply displaying a text file. There are many ways it can be invoked (or cause it to be displayed).
One place is from inside /etc/pam.d/sshd where there is a line for the motd:
`` session optional pam_motd.so # 11
Commenting this out will disable the motd from being displayed. Another place the information can be stored is in the profile file located in /etc/profile.
It is also in the sshd configuration file (/etc/ssh/sshd_config) so don't forget to update that and then restart the sshd service (/etc/init.d/sshd restart) for any changes to you make to the config file.