Andem - 12:18 am on Jun 11, 2013 (gmt 0)
I decided last year that forums are not a very good candidate for AdSense and have completely abandoned trying to monetize them.
If you insist on running AdSense on forums, I highly suggest you have some kind of automatic filter in place to prevent ads from displaying on pages having to do with anything relating to what their policies are against. (IE: hacking,cracking,serials,keygens,violence,murder,stabbing,death,etc.)
If you don't have adequate programming knowledge to implement something like this, I suggest hiring somebody to do it for you and then shoot them (AdSense support) off an email to let them know *exactly* what you've done to comply with their program policies and terms of service.