Bloomberg reports:

The U.S. Securities and Exchange Commission is probing whether credit-rating companies changed the way they graded debt as the market for products tied to subprime mortgages boomed earlier this decade, its chairman said.

``The volume of the structured-finance deals that were brought to the credit-rating agencies increased substantially from 2004 to 2006,'' SEC Chairman Christopher Cox told the Senate Banking Committee today. The regulator is looking at whether the companies ``adapted their rating approaches in this environment,'' Cox said.