Many (not all) AdSense publishers saw CPC plummet this weekend. Drops of up to 75%. The issue has apparently been resolved with some advertisers being blacklisted. Here is the closest thing to a statement from Google:
Quote"Hi everyone. After chatting with a number of folks on my end here is where we are: Over the past 48 hours, a number of AdSense publishers alerted us to an issue with declining cost-per-click for ads on their sites. We were able to identify the cause of the issue quickly and resolve it quickly: Several ad buyers were using irresponsible campaign parameters, lowering query coverage for specific creative types in some countries. The ad buyers responsible have been blacklisted and impacted publishers should see that their coverage is back to normal in their AdSense account."
Anyone care to guess at what "irresponsible campaign parameters" would lower query coverage for specific creative types in some countries ?
I knew of people buying cheap in one country and arbing to US.
The targeting was the trick.