Those who you witness, or suspect, of violating the Ghosts Online Code of Conduct in-game are to be reported in-game. This is the official and most direct course of action that you can take regarding this issue.
Clans suspected of cheating are to be reported to Beachhead via their Twitter handle. - Beachhead Studio (beachheadstudio) on Twitter
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Modern Warfare, Black Ops, Ghosts