Since the housing market started to soar in 2001, mortgage fraud has become the fastest-growing white-collar crime, according to the FBI. Last year, crooks skimmed at least $1 billion from the $3 trillion U.S. mortgage market.

Now that the market is slowing, fraud is only rising. As business dries up, there's increasing pressure on lenders, brokers, title companies and appraisers to be profitable. That means loan and title documents aren't scrutinized as carefully as they might be, and courts can't keep up with the volume of paper. Then there's the mad rush by many to sell, particularly by people who paid high prices for homes, and suddenly can't afford the mortgages.

It's like a tasting menu for con artists, so tempting that in some cities drug dealers have turned to mortgage fraud. Here are three types of mortgage fraud and how they work.