The Google Japan Webmaster Blog announced that they have penalized a link network there for trying to manipulate Google search results rankings.
Google translate tried to translate the blog post - not too well from the looks of it:
As part of this effort, Google this time, in order to operate illegally search result link program has undergone a countermeasure against some of the site network of the Japanese had done the buying and selling of participating in the link. Among this is because it was also included sites that repeatedly Webmaster Guidelines violation, was subjected to severe measures than normal in some cases.
The blog post added:
In addition, we tell even before, there seems to be the case that measures would be carried out, such as violation of the Webmaster Guidelines in place without the knowledge of the webmaster. Previously it introduced the example of SEO firms , but it seems there is also be generated by the outsourcing of such advertising not only SEO skilled in the art. In order to prevent this, the web master you we recommend that you check from time to time and see whether subcontractors are doing what measures.
It has been some time since Google publicly claimed to go after a link network. They've done so in Germany and large agencies in Germany and penalized networks in Germany, Italy and Spain in the past. They've targeted Poland and many other countries in the past and many other link networks both in the US and worldwide. but it has been a while since we had one of these.
Those in Japan, check your Google Search Console message center.
金谷 武明 Takeaki Kanaya from Google announced this on Twitter saying:
Forum discussion at Twitter.
H/T SEM Post.