343 Industries plans on bringing the Flood back to Halo through a mode they cleverly titled 'Flood'. While this isn't anything new, the details released today certainly are.
'Flood' is much like infected in that it places Spartans against the enemy. In this case, the Flood. The objective is to not be turned/taken over. According to the devs, "Flood is the spiritual successor to Infection, a fan-favorite game type from Halo 3 and Reach. Our goal was to recreate it and push the mode to be new and different from previous versions."
This is going to be a very welcome game mode.