I would recommend that you provide at least some 'hypothetical' details to give a sense of what you are talking about and what you stand to lose (or not). That said, if there is any wrong doing, it is of course a perfectly understandable to want to denounce it. If this is what you wish to do, I would suggest that you simply call AA or send them a letter detailing what you know with as much precision as you can. As you say, if someone is defrauding AA, it should enable them to track him/her and put an end to their unsavoury activities. As others have pointed out, if you yourself behaved in a way which is contrary to the terms and conditions that you have signed up to, there is a risk that you AA decide to react to your own wrongdoing as well (which could end up in your losing some miles or in your own account being terminated) although it is also possible they decide to be lenient if your confession enables them to catch a much bigger fish, it is hard to know without any sense of what you and he/she have done.