Leet:
Also known as L337 or L33t or 1337. This is (amongst other things) a language used in chat rooms where letters are replaced by numbers and symbols (Iri5h J4ack for example). Words may also be mispelled.
It's a programmer's joke (I use the term loosely) and is apparently buried in a number of BBS software packages, in various guises.
So here, when the post count reached 1337, it states "leet". As another example, enter "BBS software leet" into Google. In the list of matches, it will highlight those words and the numbers 1337 and 337.
Programmers! Who'd have them?
Programmer's mothers