S&P and Moody's were collaborating since at least 2000 on the pricing of the so-called "esoteric" structured instruments associated with mortgaged-backed securities that caused the 4Q07 crash. They collaborated via the competitive intelligence firm Washington Information Group (which does not seem to be around anymore.) The collaboration was almost certainly illegal (IANAL). They did this because neither wanted a price war when rating these. I did sign an NDA with S&P that kept me out of the industry for two years. I left the industry shortly after that and went back to what I used to do.