An influx of securities backed by subprime mortgages is exposing investors in collateralized debt obligations to increased risk, a new report by Fitch Ratings suggests. “Structured finance CDOs may experience loss of excess spread from subprime residential MBS collateral, downgrades or writedowns on subprime RMBS collateral in extreme scenarios as borrowers with ARM products experience payment shock at their reset dates,” Fitch warned in an Aug. 21 report...