BAN_UNBAN
These commands prevent anyone from a site with a hostname containing the
site substring from logging in to the game. You may ban a site to ALL, NEW
or SELECT players.  Banning a site to NEW players prevents any new players
from registering.  Banning a site to ALL players disallows ANY connections
from that site.  Banning a site SELECTively allows only players with site-ok
flags to log in from that site. Ban with no argument returns a list of
currently banned sites.

Unban removes the ban.

ban [<'ALL' | 'NEW' | 'SELECT'> <site>]
unban <site>

> ban new ai.mit.edu
> unban ai.mit.edu