John Mueller covers Black Hat Spam, https signals, url formats, manual actions and more.

Google: We Do Take Action On Black Hat Spam In Spammy Niches

There are certain industries and niches on the web that are somewhat reserved for black hat SEOs, SEOs that go above and beyond and push the line of what is outside of the Google guidelines. Some people call these areas PPC, standing for porn, pills and casinos.
by Barry Schwartz
Search Engine Roundtable