How to report harassment taking place within Blizzard chat.
How to report a player for cheating in Diablo III
Reporting your own behavior won't prevent action.
How to report harassment in Battle.net Groups
How to report players in Diablo III.
Reporting an Exploit or Hack
Information on how to report forum posts
Reporting another player that is using an offensive or inappropriate BattleTag
Information regarding harassment for streamers
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