I work in Online Media, while it is common to have these types of issues it is uncommon for Google (Doubleclick) to have these issues. If you are using third tier banner partners then it is possible.
My two thoughts are A) look into third party malware scanning companies Dasient was one we worked with for a long time until they were bought by Twitter. B) if u are using Google and their ads are getting you flagged then to me it would seem intentional. If you can locate who purchased the ad then you can pursue them with C/D and other legal means if you desire.
Keep up the good work!
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