This week Moodys Investment Service downgraded its ratings on a total of $42.2 billion of residential mortgage-backed securities (RMBS) made up of subprime home loans.

The agency said the downgrades are a result of “continued performance deterioration in subprime pools,” which is likely to worsen further as still-falling home prices and high unemployment trigger more defaults. The ratings actions reflect Moody’s updated loss expectations on subprime securities issued between 2005 and 2007.