ps and wall; How do they work?

[For Mongo]

In article <13850 at smoke.BRL.MIL>, gwyn at smoke.BRL.MIL (Doug Gwyn) writes:
>>2)  Even after I do 'mesg n' or 'chmod og-rx /dev/tty?', other
>>    users can still send me message through command 'wall',
>>    how come?  Is there anyway to prevent 'wall' from sending the
>>    message?
> 
> Any version of "wall" that writes on terminals that have had "mesg n"
> executed on them is BROKEN.  You can fix that by removing /bin/wall.
Ummm.... Isn't wall only usable by people with system access priviledges, which
will just ignore the mesg?  And, it would be difficult for him to fix it,
because I am guessing (from his previous question) that he is not a SysAdmin.