Modifications made to Halo, either through modchips or other means.
The advent of modchips and hardware hacks for the Xbox have meant even more interesting things have been found out about Halo in recent days and weeks-- even things that fansites have been discussing for a long time and thought were impossible.
Louis Wu at HBO brings word that BOLL and Phforslayer have colluded to replace the first warthog in the level "Halo" with a Banshee-- which is flyable, something long thought impossible on that level. Not to be outdone, BOLL went ahead and posted screenshots of the Engineer model in HBO's forum, in engine-- again something that long was thought not to exist in the game as shipped.