Usage: ban [<all | new | select> <site>]
       unban <site>

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.

Examples:

  > ban all whitehouse.gov
  > unban ai.mit.edu