Short for 'All your
base are belong to us', meaning something like 'we own you' or 'you got owned' or something. anyway. The popularity
of this phrase is unexplainable but it has circulated the net for years in pictures and text. Originally comes from
a game for the sega megadrive system called zero
wing, a space shoot-em-up released in japan
in the '80s. The game was translated into english (very poorly at that, it almost qualifies as engrish) and released in europe in 1989. For more details on how this phrase came to be, google for 'AYBABTU'.