The underlying portfolio of securities that backed the synthetic collateralized debt obligation (CDO), named "ABACUS 2007-AC1," was connected to the performance of residential subprime mortgage backed securities (RMBS). The SEC complaint alleges it was not disclosed to investors that "a large hedge fund, Paulson & Co. Inc. ("Paulson"), with economic interests directly adverse to investors in the ABACUS 2007-AC1 CDO, played a significant role in the portfolio selection process."