from
Jargon File (4.4.4, 14 Aug 2003)
pr0n
//
[Usenet, IRC] Pornography. Originally this referred only to Internet
porn but since then it has expanded to refer to just about any kind.
The term comes from the {warez kiddies} tendency to replace letters
with numbers. At some point on IRC someone mistyped, swapping the
middle two characters, and the name stuck. It then propagated over
into mainstream hacker usage. New versions of the Mozilla web browser
internally refer to the image library as "libpr0n". Compare {filk},
{grilf}, {hing} and {newsfroup}.