The default risk on 489 bonds backed by residential mortgage-backed securities prompted Fitch Ratings to slash the bonds’ ratings this week.

The bonds are part of 291 different residential mortgage-securities deals.

Fitch moved the bonds to ‘Dsf’ status—a ratings level that generally suggests the occurrence of a principal write-down.

Prior to the downgrade, the impacted bonds maintained ‘Csf’ or ‘CCsf’ ratings.

Fitch says ratings below ‘Bsf’ usually signal a coming default.

The New York-based ratings giant says 227 of the bonds are classified as Alt-A, while 187 are prime and 62 are backed by subprime loans.

About 51% of the distressed bonds have a recovery estimate on the principal balance in the range of 50% to 90%. Another 37%  have a zero percent recovery rate, suggesting deep distress.

Most of the bonds in the report were issued after 2004, with a large majority issued in 2007.

The deals are linked to Countrywide in many circumstances, with a large number of bonds labeled as CWALT transactions. CWALT is short for Countrywide Alt-A.

Click here to see a complete list of the bonds impacted by the Fitch downgrades.

Write to Kerri Panchuk.