Forum:What is the scourge?

Spoilers.................We know from ME:A that the scourge is a dark energy phenomena originating at Meridian station and that the Khett are not responsible for it. Since dark energy is a recurring theme in the original trilogy I am wondering how it ties in ( if at all) with ME:A. Was the scourge an experiment gone wrong or was it deployed by an unknown enemy possibly originating in the Milky Way?

-Technoir