Bungie has finally scrapped CD checking in old-timer Halo 1 for PC, feeling five years of spinning may have ruined your discs.
This will be coming in patch 1.08, which will be mandatory from Friday onwards, according to the Bungie website. Other fixes address server-crashing bugs but nothing else; the game is too old to bother combatting aimbots in, apparently.
Anyway, Bungie doesn't officially support Halo 1 PC because Microsoft owns the game. This patch was made as a favour to the community.
However, don't expect too many more fixes in the future or for source code to be opened to the internet.