A word that derives from the hacker elites, leetspeak not only relies on humor and improvisation but also is a new kind of language now popular in the hacker community. Leetspeak, generally also known as L33T speak, incorporates layers of computer underground references—slang words such as warez (meaning pirated software), for example—and transforms the letters in the slang words into numbers and symbols (called visual puns or icons).
As examples, the letter E is written as a 3 and the letter A is written as a 4. Also, L is written as a 1 and an S is written as a 5. Consistent with earlier TAP methodology, the letter O is written as a 0. Technically speaking, leetspeak is a cipher on top of jargon: Slang words that are incomprehensible to those outside the hacker community are further rearranged into symbols. Other fun consists of alternating uppercase and lowercase letters and deliberately misspelling common-usage words. For example, porn will often be written as pr0n and the as teh.
Hacker community jokes are designed to fool not only people but also machines. The technique called “fat-finger typing” is what spammers use to circumvent filters on email. Fat-finger typing makes a word usually readable to a human (who can mentally adjust for errors in the typing and “see” the word as it should be) but unreadable to a search engine. Because search engines are not blessed with the cognitive flexibility and adaptation of humans, fat-finger typing often lets undesirable things such as pornography ads get through software filters.
Smith, R. Virtual Culture: Hackers Devise Their Own Language Literacies. The Globe and Mail, July 22, 2004, p. R1, R3.