. the mortgage loans underlying the non-agency securities are generally non-conforming ( i.e. , original balances in excess of the amount qualifying for agency securities ) and predominately have interest rates that are fixed for a period of time , after which the rate adjusts to a floating rate based upon a contractual spread that is indexed to a market rate ( i.e. , a 201chybrid arm 201d ) , or interest rates that are fixed for the term of the loan