I wish I knew.

It's an OldSchool 'computer cracker' thing, I think; sometimes called 'l33tsp34k', the point is that 'haxx0rs' could write in it and other haxx0rs would be able to understand it, but mere mortals obviously didn't have the brain power to work that one out.

0h n0, wh4t3v3r sh4ll u5 m3r3 m0rt4ls d0.

Google in leetspeak:

lib/main.php:944: Notice: PageInfo: Cannot find action page

lib/main.php:839: Notice: PageInfo: Unknown action