S&P Revises Opinion on Performance of Subprime Loans: 'These changes were made to better cature the deteriorating performance of pools from 2006 and late 2005.'.

NEW YORK -- Rating agencies have continued to home their assessment of troubled nontraditional mortgage securitization vintages from 2005 and 2006 and related collateralized debt obligations.

Standard & Poor's Ratings Services has downgraded 498 of the 612 classes of residential mortgage-backed securities that it placed on CreditWatch with negative implications July 10, and it has corrected the value and status of the securities.

S&P said the 612 classes, rated from the fourth quarter of 2005 through the fourth quarter of 2006, represent $7.35 billion of securities, not $12.02 billion as originally reported.

The downgraded classes, representing $5.69 billion in securities, are backed by first-lien subprime mortgage collateral.

S&P also left 26 of the first-lien subprime classes on CreditWatch and affirmed the ratings on 74 classes and removed them from CreditWatch.

Of the remaining 14 classes, the ratings on nine were affirmed and removed from CreditWatch "because they involve alternative-A mortgage collateral and were not intended to be included" in the July 10 rating actions, and five were left on CreditWatch because they are backed by closed-end second-lien mortgage collateral and will be reviewed later by S&P, the rating agency said.

Meanwhile, S&P also downgraded 64 other classes backed by first-lien subprime mortgage collateral that involve CreditWatch actions taken before July 10 on 70 tranches of RMBS.