financialhost - 4:10 pm on Oct 8, 2012 (gmt 0)
Perren - I can't be certain it was Penguin, but the timing of page shifts coincided with Penguin 1 & 2, and yes, penalising on the basis of backlinks makes negative SEO easier (there have been a number of posts in earlier threads on this).
So Google creates a situation where all your competitors build lots of links to de-rank your site and the results will eventually be:
All good sites will no longer rank
The good sites will get a link boost and rank well in Bing & Yahoo.
Users see results are no longer good in Google and move to Bing & Yahoo.
Moral of the story - karma gives out what it gets.