Denver-based Allonhill, a mortgage due diligence and credit risk-management firm, will perform third-party reviews on residential mortgage-backed securities (RMBS) for Standard & Poor's Rating Service. Allonhill said in a statement Tuesday it received approval from S&P to act as a contractor in performing due diligence on publicly traded RMBS. The approval is part of a program designed by the rating agency to allow companies to identify third-party review firms that meet S&P standards of accuracy and independence. It comes after S&P announced more stringent policies on its ratings in '08 — including a new assessment for third-party review firms — following ratings scrutiny in the wake of the mortgage collapse when triple-A securities faced downgrades, according to Allonhill.