I got 2 unnatural link notices for my sites.
I was very interested to know which ones, since I have removed webmaster tools from all my sites a few months ago.
So I log into my site, I look and see there are NO sites in my webmaster tools listed (as I have deleted them all).
Then I look at the sites that apparently have "unnatural links".
To my amusement, those sites were "dead" failed projects that I stopped linking to over 2 years ago.
So I don't know what Google is on about, because any link I would have received would be 100% natural.
This proves that they are really grasping at straws and trying to scare you.
Their algorithm is not as ninja as they want you to believe.