In first quarter of 2102 Google has sent around 7,00,000 message to website owner though webmaster panel that their site is using black hat method of SEO or having unnatural incoming links and advice them to correct it. It created a lot of confusion and all SEO and webmaster start 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 it 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 send more clarified mail so that site owner should know exactly for what they have be warned.