While watching the Halo 3 teaser trailer, like i do every morning when i wake up, I noticed that the trailer has slightly changed. During the part were the cortana like voice says "This is the way the world ends." a large hazy blue sqaure appears on the screen for a noticable amount of time.
There is much speculation that this is another viral marketing campaign, but others think it may just be a video glitch after the update. The teaser does not require a re download to see it either as it was updated during the Spring update