If you noticed your AdSense CPCs decline last Sunday (the 5th August), you were not alone. In a statement from a Google rep over at WebmasterWorld:
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 issue 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.
Now, Google has confirmed they have dealt with the situation and have blacklisted the ad buyers that were responsible.
Essentially, ad buyers were able to manipulate AdSense causing a decline in Cost Per Clicks for publishers. It meant a decline in coverage of the ads and a drop in the fill-rate. This has all been identified and rectified by Google, although, publishers will not be able to recover lost revenue over the period.
What does this mean for digital marketers? Basically, don’t be dicks! Just because you find a way to exploit a system for your own gain, do not, and I repeat DO NOT use it. The consequences are not worth the short term gain.