With interest rates at exceptionally low levels in recent years, borrowers have been reluctant to choose adjustable-rate mortgages. For those opting for ARMs, hybrids remain the most popular, according to results from the annual ARM survey recently released by Freddie Mac. ARMs accounted for 4.6 percent of the $921.72 billion in mortgage-backed securities issued by Fannie Mae, Freddie Mac and Ginnie Mae in 2014 ... [Includes one data chart]