Rasputin - 7:21 am on May 15, 2012 (gmt 0)
My hobby site was hit - nothing like active link building, but had a few ezinearticles from a couple of years ago linking to it (only about 5) and 2 sitewide link exchanges with very relevant sites dating back 4 years. Not excessive IMO! Site has plenty of natural links, facebook likes etc since.
But...the owner of one of the 2 link exchange sites has at some point added (presumably sold) a big 'payday loans' link in the middle of their homepage, completely unrelated to the site. Maybe that made them a bad neighbourhood? (Unfortunately I now can't get hold of them to get our link removed).
So either just one external link was the problem, or it is on-site factors.