Manny, your case sounds almost the same to mine.
I want to throw out a few more data points, and also thank everyone who's responding to this thread since I am going through something very similar.
I have several websites that obtain backlinks in a very similar manner. My largest site was hit Friday night, losing position for 222 keywords that I have been strong for the past couple years. It seemed to get hit by page. In other words, if a page was hit for one keyword it was also hit for several others. Conversely, I have some pages that were not hit at all.
A smaller site was also hit Friday night. Because it is a smaller and newer site, every page/keyword seemed to get wacked.
No messages in WMT for either of the two sites (yet).
A third site, that happens to be in a different WMT account (which I always access from a different IP) was hit and did receive the notice about external links. Oddly, this site has the least amount of aggressive backlinking. The site had never done well, and I gave up getting links about 6 to 12 months ago (there may still be some automated stuff going on though).
A fourth site, in the same WMT account as above, was hit hard Friday but did not get a notice.
- All of these are retail ecommerce sites with all unique high quality content. The sites themselves are squeeky clean.
- The backlinks use a high variation of anchor text. Backlinks point to various levels of the site, but mostly category and product pages.
- All of these sites obtained most of their backlinks through private blog networks using spun or semi-spun content. From time to time I have used all of the more well known blog networks.
- Most of these sites have a few blogroll links on blogs that are pretty spammy looking (spun content and long blogrolls).
- A small portion of our backlink pages (2nd tier) were reinforced by using some not-to-clean methods such as automated blog comments.
My intuition tells me that the blogroll links played a large part in this. However, the one site that actually received a notice does not have any.
So, I believe it was caused through some of the private blog network links. Perhaps one or more of these networks was recently compromised by Google. These links are unfortunately impossible to get rid of.
I suspect a certain blog network that everyone has surely heard of, but I don't want to list any specific services or networks as I could very well be wrong.
Now, what to do about it? I'm piecing together a plan, but I largely don't have a clue at this point.