Two growing trends in the U.S. housing market are "vampire" foreclosures, in which the bank has seized a property but the previous owners continue to live there, and "zombie" foreclosures, in which the owners have abandoned the property but still own the title, according to RealtyTrac.

The online foreclosure marketplace said the two phenomena are "monsters threatening the housing recovery."

Of the two, zombie homes are the more unsightly, RealtyTrac said. "Often these homes are more obviously distressed, falling into disrepair with no one to perform regular maintenance and upkeep. As such, they often represent a threat to the quality of the surrounding neighborhood, dragging down home values."

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As for vampire homes, those properties often appear normal and well-kept, but they add to shadow inventory that banks must get off their books, and could be a drag on recovering prices.

Florida is the state that appears to have the most of both kinds of foreclosures.

RealtyTrac said the metro areas with the highest volume of zombie foreclosures are Tampa, Jacksonville, Fla., and Las Vegas. The areas with the most vampire foreclosures are Miami, Houston, Los Angeles and Cincinnati.

Daren Blomquist, vice president of RealtyTrac, told CBS MoneyWatch, "This distressed inventory is artificially being held back so that in the short term, it's helping boost the home prices and the housing recovery in general. But the red flag there is that eventually these homes are going to have to hit the market. They're not going to just disappear."

MoneyWatch said both kinds of foreclosures total about 400,000 homes in the United States — about 10 percent of the current volume of home sales.

The Washington Post reported complaints against banks by struggling homeowners are growing, and that government officials are pressuring some of the country's biggest banks to improve the way they handle mortgage relief programs.

This week, a court-appointed overseer of the $25 billion national mortgage settlement with large banks added more requirements for erasing shortcomings in the banks' foreclosure operations. Also, the New York state attorney general's office filed a lawsuit against Wells Fargo for allegedly violating the terms of the settlement, the Post said.

The banks under official scrutiny include Bank of America, Citigroup, JPMorgan Chase and Wells Fargo.

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