They were "classified" in ODST; but in order for them to be deemed as "classified," they have to be discovered first. The Huragok also appeared in Halo Wars as a means to repair Covenant vehicles, and that takes place even before Reach. They were known to exist, but their existence was simply not made known to all of the troops. Interestingly enough, the Jiralhanae are in a similar situation. They appeared in Halo: Reach; but according to the novel "Halo: First Strike," John-117 had no idea what a "Brute" was when Cortana intercepted a Covenant transmission on the Unyielding Heirophant on their return to Earth from Installation 04A.
The huragoks existance isn't really classified it has been sighted numerous times throughout the books, it's just that the huragok in H3:ODST was very important because of the classified information it contained. Cuz it can duh!!Their existance wasn't classified before the events of ODSTI believe that the actual line in the game is referring to the 'Great Schism', the civil war between the Elites and the rest of the Covenant. However, their technical neutral stance means they aren't even supposed to be deployed as front line warriors, so they wouldn't have been encountered on a regular basis in combat. Maybe they only appear on Reach because the Covenant were certain of victory, and on Earth because the Covenant didn't expect a fight.hkjl\just because its classified by the unsc dosent mean the covenant woudnt bring them to reach
spartans are even more classified.The Huragok have been in the Covenant since before Halo: Reach, their existence has been "classified" because they we're mere slaves to the Shan'Shyumm, and we're rarely seen or taken captive because the Covenant attached bombs onto them for the safe keeping of their knowledge.Because the events in Halo 3:ODST take place only about 2 months after reach, meaning that the Huragok could still be kept under wraps.