goodroi - 5:09 pm on Aug 22, 2013 (gmt 0)
This is a good reminder that link optimization is not always concentrating anchor text but for some sites it is about diffusing anchor text to avoid triggering a false positive.
I know you and your team are constantly monitoring your site. Just to be safe have you run a scan of your entire site to identify all outbound links? Mistakes do happen, so maybe some spam pages slipped through without your team noticing. Worst case your site was hacked and this content was added. Either way, regularly running a scan on your site will help to spot innocent mistakes and malicious hacks.