Sorry about the delay on the 1337 thing.
Quick history lesson - going back to the day (20-25 years ago now, before the Internet as we know it), there were NPD or "elite" BBSes that had cracked software, .exe files, etc. for download. Usually, you had to know someone or be introduced to the sysop (the BBS operator, what we typically call an admin now) before you could gain access to reduce the risk of prosecution / litigation, etc.
A lot of BBSes like this focused on hacking - trading passwords and logins, instructional files, etc. The more hackish BBSes could develop a membership which substituted numbers, characters and so forth for letters, as well as mutating words - think of it kinda like a variant of Pig Latin. Thus, elite became 1337 on such boards - 1 = L, 3 = E and 7 = T. That's why you guys @ for A, why you use $ for S (although 5 is also acceptable), etc. Typically, it focused on how words were pronounced, not their spelling, so you get things like 1337-5p33k. Numbers and letters could be assumed to flip, international characters could be brought in, characters could be assembled from slashes and pipes and other punctuation marks - basically, it was a language based in English that more closely resembled a mashup of Cyrillic, Scandinavian languages, German and what often looked to the uninitiated like computer code.
Now, I'm sure Wikipedia has an entry on 1337-5p33k (aka leet speak), and this is a tech forum so you'll likely find people who have different opinions about it, but this is how I saw it come to pass. And, at the time, it often seemed to be script kiddies who used it most. I'm sure Wikipedia has an entry on script kiddies too
