I was playing halo2 campaign on my 360 and I noticed that some images get burned into the screen. I snapped pictures of the arbiter's silhouette, burned into the left side of the screen. One of those bigger forerunner robots also got burned into the screen.
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It's a problem with the 360's software emulator, don't listen to anyone who thinks that your 360 is broken or it's your TV. It will happen to anyone that plays on a 360.