In the first quarter of 2102 Google has sent around 7,00,000 messages to website owners through the webmaster panel that their site is using the black hat method of SEO or having unnatural incoming links and advising them to correct it. It created a lot of confusion and all SEO and webmaster started removing the links. Even they are sending mail for removal of good links. Matt Cutt issued a clarification on this
I wanted to clarify a misconception about those messages. A lot of people assumed that most or all of the 700K messages were related to “unnatural link warnings” that some site owners received.
In fact, of the messages that we sent out to site owners, only around 3% were for unnatural or artificial links. So just to be clear, of the 700,000 messages we sent out in January and February, well above 600,000 were for obvious blackhat spam, and under 25,000 of the messages were for unnatural links.
The clarification says that only 25000 sites are warned for unnatural links which will give relief to most of the site owners. Now question again is which sites are having unnatural links How to identify. I think Google should have sent more clarified mail so that site owners should know exactly for what they have been warned.