133t speak originated with hackers and gamers in message boards and chat rooms. Because they did not want other people to get involved in the topics that they were discussing, they devised a way to defeat text filters at a time when people searched for topics on message boards.

They did this by substituting symbols and numbers for letters of the alphabet. This worked because Internet users used exact words to search for items through a text filter. Therefore, if topics and words used in a discussion were spelled in code, no one would be able to find those discussions unless they knew the 133t language. At the time, knowledge of 133t was limited to only a few elite computer literates. As a result, 133t was also called LEET, which is a shortened form of the word "elite" and is also what the characters 133t spell out in this code.

Although there are no specific rules for 133t speak, there are conventions. For example, vowels are usually replaced with numbers. The rule is that as long as the number resembles the intended letter, it is acceptable.