如何检测iframe(跨域)中的单击?即防止点击欺诈

I got a warning by my ad system provider about click fraud. No further info, all they are recommending is "hide the ads for users who click on ads too quickly'". I wrote a piece of JS script that hides all DIVs with ads for N seconds (using cookie) when clicked on, but this solution does not work as the "inner" content (with ads) is generated by an JS script that calls and renders the content from external server (as you would expect from an ad system). So, when one takes the cross-domain security into account it is kinda Catch 22. How can I detect a click inside a DIV (locally defined) of which content is rendered by an external JS and in iframe? I got a warning by my ad system provider about