The developer has just pulled credits from thousands of players who "egregiously" exploited a glitch in the game that artificially inflated the number of credits they had.
"Specifically, we targeted an exploit that allowed players to complete a Challenge 20+ times via itentional [sic] network manipulation (i.e., disconnects)," wrote Bungie on its website.
The company did not specify exactly what the glitch was, but it shows a real crackdown from Bungie on people who manipulate the game in a way that makes it unfair to other players.
This comes just a couple months after Microsoft banned the Xbox Live accounts of people who illegitimately obtained a pre-release copy of the game.
Clearly, the guys behind the scenes at Halo Reach are making game legitimacy a real concern. So if you really want to gain an illegal advantage in a game, go do it on something that has no policing. Like Uno.