Google lowers PageRank penalty paid link

Google has long claimed to punish the SEO (Search engine optimization) for the purpose of the paid link, these days has been the axe, I often visited several well-known foreign blogs have been recruited, PageRank by Google down to 4 or even 3.

According to Zac, websites punished by Google include:

WASHINGTONPOST.COM/PR7 to PR5
Statcounter.com/pr10 to PR6
AUTOBLOG.COM/PR6 to PR4
ENGADGET.COM/PR7 to PR5
PROBLOGGER.NET/PR6 to PR4
COPYBLOGGER.COM/PR6 to PR4
SEARCHENGINEGUIDE.COM/PR7 to PR4
SEARCHENGINEJOURNAL.COM/PR7 to PR4
JOHNCHOW.COM/PR6 to PR4
QUICKONLINETIPS.COM/PR6 to PR3

This one I see a lot of IS, ProBlogger, Copyblogger, Johnchow, Quickonlinetips, Engadget, did not expect these famous bloggers will be Google brandished down, Want to Google is never afraid to offend bloggers, even if offended and how?

What I'm wondering is, how did Google detect that a link is a paid link? Manual detection code? If the link does not add the word "sponsorship" or "advertising", how does Google know that the link is a paid link?

Therefore, I suggest that if a site PR is relatively high, then do not clearly on the page marked the sale of links, and so on, do not recommend to participate in text link ads such a trading platform, so as not to be punished by Google downgrade.

Update: October 28, ProBlogger, Copyblogger and other well-known blog PageRank back to normal.