Sites affected by this change might not be easily recognizable as spamming without deep analysis or expertise, but the common thread is that these sites are doing much more than white hat SEO; we believe they are engaging in webspam tactics to manipulate search engine rankings.
The change will go live for all languages at the same time. For context, the initial Panda change affected about 12% of queries to a significant degree; this algorithm affects about 3.1% of queries in English to a degree that a regular user might notice. The change affects roughly 3% of queries in languages such as German, Chinese, and Arabic, but the impact is higher in more heavily-spammed languages. For example, 5% of Polish queries change to a degree that a regular user might notice.
We want people doing white hat search engine optimization (or even no search engine optimization at all) to be free to focus on creating amazing, compelling web sites. As always, we’ll keep our ears open for feedback on ways to iterate and improve our ranking algorithms toward that goal.