Edge - 7:30 pm on Mar 21, 2013 (gmt 0)
Why is everyone assuming they were AdSense sites? The CTR is incredibly low and unless I've missed something over the years AdSense is primarily a CPC network. Plenty of CPM networks out there that would fit the parameters described and they're probably a whole lot less sophisticated that Google when it comes to detecting this sort of activity.
My site got hit last year by a botnet that sounds like this one. They hit five specfic adsense webpages. If the botnet owner excluded my site from thier ads they could in theory run up the costs of competitors but not thier own.
It's all about ROI..