Code:
if ($regex($nick,^..?$)) {
  ban -u60 ?!*@*
  ban -u60 ??!*@*
  kick $chan $nick possible Botnet (no nicks shorter than 3 chars allowed)
}

Please be more specific about "letters" if this isn't what you are looking for smile
Atm, it will match nicks like: a ^ b1 c_ [] |x 33

Note that I changed the ban part, too: banning all nicks made of one or two chars. (Of course, you can keep your ban on *!*@host.domain. If it's a botnet, you might flood yourself off the net if setting tons of bans too fast).


If it's only about nick length, you could use the simple: if ($len($nick) < 3)