To put it as simply as possible when the forerunners created the rings they also created shield worlds. These shield worlds were refuges from the affects of the halo rings one of the forerunners informed the flood of this so the flood went to one shield world and survived on beings who were living there. Later the covenant discovered this world tried to use the forerunner fleet on the surface of this shield world the UNSC followed and got inside purely accidentally, as seen on Halo Wars. Therefore freeing the Flood. Hope that helps :)
Chat with our AI personalities
THE halo games that have the flood are halo combat evolved,halo 2,halo 3 and halo wars
halo 1,2,and 3
No.
The Flood was actually contained inside Halo before some Covenant set them free. Their actual origins are unknown.
its possible