Forerunner fleet weaponry 1

It soon became clear to the Forerunners that ordinary naval tactics would prove fruitless in stemming the mounting infection. They decided their only hope of defeating the parasitic swarm would be to create even more lethal weaponry. At first, robotic drones were sent to battle and contain the Flood onslaught using surgical, localized tactics. Soon after, the Forerunner Fleet Command considered “premature stellar collapses,” by which a supernova would be triggered by a naval battle group, engulfing a planetary system and preventing any possible risk of Flood infection.
(Halo Encyclopedia; pg.169)

It is my opinion that any system where there is evidence that the enemy has established a physical presence is lost and must be razed. This fleet currently retains the capacity to force premature stellar collapse; I advise that this be established as standard operating procedure for all compromised systems forthwith. We cannot fight this war by half measures if we intend to win.
(Halo 3; Terminal 2)