Hatena is a Kyoto-based company that has run several web services since 2001. Similar to Digg, Delicious or Reddit, it has grown a web-savvy, tech-oriented community around a Q&A service (from which its name, Japanese for "question mark," is gleaned), free blog-hosting, and so on.

While its user base is not huge, it offers some much-loved tools. Hatena Bookmark, with which users may record favorite web pages with a short memo, is the most popular online bookmarking service. Because a news story that is bookmarked by a large number of Hatena users attracts more attention, websites of Japanese media outlets such as Nikkei and Asahi display a Hatena Bookmark button on every single news page and have done so for years — even before similar buttons for Twitter, mixi and Facebook were introduced.

However, earlier this month, some bloggers discovered that these external bookmark buttons have been sending site visitors' access information to MicroAd, a web advertising company that runs behavioral targeting advertising programs. This has been happening since last September, when Hatena modified its button program with very little fanfare.