Long post is long, but oh well. Although there isn't any direct quote stating so, alot of the time the UNSC has no idea [i]what[/i] or [i]who[/i] is coming out of Slipspace, leading it to be an "anomaly" in Lamen's terms. I'm pretty positive I remember Auntie Dot telling Noble Team that there was an abnormal amount of Slipspace Anomalies above Reach, actually turning out to be a Covenant fleet. [quote]In addition to that, the Spirit of Fire sacrificed its slipspace engine to destroy Shield 0459.[/quote] It may not have a Slipspace drive, but it does still have power and most likely engine thrust if the ship managed to slingshot away from the planet. 20+ years is nothing to the Flood, so while the crew jettisoned themselves out, the Flood assumed direct control of the rest of the ship and suited it to their own ends. Without anyone even knowing of their existence in deep space, its entirely possible they made their rounds and have been causing some trouble. There was and still is nobody out there to stop them as the exact location of the SoF is still unknown to Humanity. Furthermore [quote]In 2558, UNSC Infinity was dispatched to rescue the long lost ship behind enemy lines after it was discovered and was being threatened by Vata 'Gajat when it arrived into Covenant Remnant-controlled territory. However, this was actually a trap laid by Daniel Clayton for Admiral Terrence Hood. The ship was not there. The Spirit of Fire was in fact still drifting through space, and had been boarded by Flood infection forms despite all the counter measures imposed by Chief Medical Officer O'Neil and was drifting towards a collision course with a planet.[/quote] For one: This means that the Flood not only survived the destruction of the Shield World as a biological entity, but also have enough intelligence to target a ship out in [i]space[/i]. For two: This quote further proves my point about the Flood defecting to a planet. For all we know, the Flood could've landed and absorbed enough biomass on the planet to either create another Gravemind or atleast an army of foot soldiers to be used by a Gravemind later. If they did create a Gravemind, the Logic Plague is even more of a viable option as a galactic threat.