Freddie Mac this week issued $1.04 billion of MBS backed by modified loans, making a small dent in the government-sponsored enterprise’s portfolio of distressed mortgages. The securities were issued under a new MBS prefix reserved just for modified loans, and Freddie officials indicated that the securities would be held in portfolio rather than sold in the market. All of the modified loans are fixed-rate mortgages, although $138.2 million of the loans were originally adjustable-rate mortgages. Most of the loan mods have 30-year terms. The loans in the first batch of mod MBS were originated...