These ratings were believed justified because of risk reducing practices, such as credit default insurance and equity investors willing to bear the first losses.

Over time, the premiums should accumulate because the risk of credit default is so small, a spokeswoman said.

Electricity, wood pulp, steel, advertising time on television, insurance against credit defaults - all became fodder for the rapidly growing Enron finance and trading empire.

"Bankruptcy or a credit default is not a concern," he said.

The score supposedly predicts the default probability of a borrower based on vast historical credit, default and personal data.

Without the good folk living beyond their means there would be no credit defaults.

"People were worried about credit defaults."

The losses were the biggest since the 1930s and reflected the impact of the recession, which had caused record numbers of bankruptcies and credit defaults.

Many of the investment banks had limited capital reserves to address declines in mortgage-backed securities or support their side of credit default derivative insurance contracts.

The credit rating reflects the probability for credit default.