Although we probably will never know 100% of the story, the main reason why HaloGen was ordered shut down was because MSGS was making Halo Wars at the same time. Of course, no one knew that Halo Wars existed at the time. In that case, it was MS making sure they could profit from their own RTS, and not have to compete with a free product. As long as Halo Wars 2 doesn't make an appearance, and you don't sell it, its unlikely that they will go after you. There are other Halo mods out there that haven't been shut down.

: Theoretically speaking... how would a Halo mod for a strategy game fare these
: days? I heard a long time ago that a Halo mod for C&C Generals got plugged
: by Microsoft.

: The reason I'm asking is I'm fairly tempted to start a Halo mod for Hearts of
: Iron (see here: http://en.wikipedia.org/wiki/Hearts_of_Iron_III ) but
: I'm not quite sure if I would be breaking copyright or something.

: Any thoughts? Thanks.