One of the biggest click frauds happens a lot with Google. Since they show their ads on individual websites, a few webmasters click on these ads to drive up their own profit. A way to prevent this is to toggle the ads so that they are only shown on the Google search engine...
At the campaign level select edit campaigns and in the top right hand side of the box you will see search network and content network... deselect the content network...
You can also narrow languages and countries to avoid ads running where you cannot service.
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