Not a good month for the ratings agencies. There's been the fuss over Moody's decision (which it is now rapidly backing away from) to change its bank rating methodology. And now Bethany McLean of Fortune, who made her name when she suggested that Enron might be unsound, writes that the agencies - all of them - may be partly to blame for the continuing collapse of the US subprime mortgage business, by rating CDOs based on mortgage debt far too highly.

Janet Tavakoli, who runs Tavakoli Structured Finance, points out that AA-rated tranches of CDOs backed by subprime mortgage paper now yield far more than AA-rated debt backed by other assets - a sign that the market doesn't trust the ratings.