There are a few different ways to cheat online including standbying which is still around surprisingly, and modding your xbox. Bungie has been keeping a close eye on cheaters since Halo 2 made it big online however they can usually play anywhere between 2 or 200 games sometimes before being caught and having their account banned. Bungie also added a way now for you to directly file a cheating complaint against the person by going to their name in the recently played list and going to "File a Complaint". Microsoft is also now implementing new strategies as well to help keep cheaters off the net. Just remember everytime they come with some new way to control cheaters the cheaters are going to find some way around it.
P.S.
The cheats at the hubpages link only work for local matches. Modding and standbying are still the only real ways to be able to cheat in an online match, be it ranked or social.