I think something they could do that would be good in the long run in Halo 2. Is have all the mplayer levels get coppied over to your harddrive... This way, if a bug is found, instead of having to deal with people that exploit it, they can now make manditory patches for the levels themselfs...
The only thing I could see bad with this is that the size of each level... But I think it is well worth it if it doesn't fill your harddrive up (completely) in the long run...
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No kidding.