In the Forerunner saga the war between Forerunners and precursors is detailed and it states that while some precursors went dormant others turned themselves into a regenerative powder which would bring them back to their forms later. But what's never clarified is if the corruption this powder suffers from turning them into the flood is due to being in such a form for so many years or if it was corrupted by being feed to the Pheru and becoming mixed in their DNA. So long question shortened is it the time spent as powder that corrupted the precursors or the unanticipated use of the powder on the Pheru that lead to its corruption.