jinnguyen - 10:35 am on Oct 23, 2011 (gmt 0)
I have a high traffic site that dropped with a similar unwanted external broken links too. The unknown sites linked to my site in a massive site wide manner. I first thought and believed that external links cannot harm us, but after I found this thread, it make me think differently from now on.
Google is broken, that's all I can say.