SEO techniques | Google targets Private Blog Networks (PBNs)
Google has taken action against PBNs which are used by black hat and gray SEO (Search Engine Optimisation) operators in their attempts to improve web site rankings through link building. Google has apparently sent out many notices warning those participating in PBNs with thin content that their site rankings may be adversely affected.
You can learn more about this topic here.
We don’t use black hat SEO techniques and none of our web sites are affected by this issue.