Leet (or "1337"), also known as eleet or leetspeak, is an alternative alphabet for many languages that is used primarily on the Internet. It uses various combinations of ASCII characters to replace Latinate letters. For example, leet spellings of the word leet include 1337 and l33t, or eleet may be spelled 31337 or 3l33t. The term leet is derived from the word elite and is also used as an adjective to describe formidable prowess or accomplishment, especially in the fields of online gaming and in its original usage, computer hacking.
The online game can be found here: 1337 Challenge!