Deva Path:

Vigil:

RoyaleWitChee:

Um i think i remember in halo 2 that gravemind or one of the oracles stating the the forerunners created the flood which is why they built the halos in case that they ever became to powerful for the forerunners to handle wich is kinda saying that they are from another galaxy or could be from another galaxy.

Nope, Halo 3's terminals made it clear that the Forerunners found them, they didn't create them.

The Flood were first found on the planet (or possible moon) G 617 g. The forerunner sent a research team to investigate the planet,but when the team didn't report for 333 hours. A medium intensity military unit was sent in, the hell broke loose.

This is from the Halo 3 ARG server 4 log transcript

"

The Conservation Measure is the only sweet note in this discordant symphony we've arranged.
{/IT'S THE ONLY CONSTRUCTIVE ACTIVITY IN DECADES OF DESTRUCTION/}
{/RESEARCHING THE ADVERSARY AS WE PROTECT THE WORTHY/}
We know that the Flood's biology is alien enough that it must be extragalactic in origin.
But where did it come from?"
{/AND WHY DID IT COME HERE?/}"

So we assume that after the flood infected much as it could in the previous galaxy, it fled to the Milky way and lay dormant on G 617 g until the forerunners contacted them. 

 

Wow, that just reminded me that i was writing a fan fic on that moon. It's probably time i started again, if you stop writing a FF for a few months people loose interest, XD