"One group, of course, would be those who have adjustable mortgages, where the interest rate can adjust and, as those interest rates have gone up in the past year, year and a half, the payments would go up," says Dr. Walden, a professor of agricultural and resource economics.

"But there is another group of folks who have had special mortgages; these are called interest-only loans," he adds. "It means that you are borrowing money to buy the house, but you are not really paying back anything on the amount borrowed. All you are doing is paying the interest.

"The problem that can result is, if you are in a housing market where housing prices actually have fallen since the time you bought the house, you could end up in a situation where you perhaps want to sell your house and you actually find that you have borrowed more and you owe more than the house is worth," Walden says.

"Those folks are really facing a tough time. It has really become a nightmare for them."