I came across the following domain name in an Adwords Display Network report (aka: content network): adsenseformobileapps.com.
According to Google, if your content network campaign is opted in to show ads on mobile devices, this is the domain name that shows up for those visitors who see and click on your ad via a mobile app.
For one of our client’s campaigns a lot of clicks were being generated without any conversions, so I added this to the excluded placements list to stop any more wasted clicks.
If you pull reports regularly, you can catch this kind of thing.
Take a look at your own content network reports (e.g check your automatic placements) regularly to see if domains like adsenseformobileapps.com are generating clicks and therefore costs, without conversions. If so, get rid of them!