Home values have taken their biggest plunge in three years, according to a report published by Zillow.com, a real estate research firm.

Economists now predict housing prices won't stop falling until at least next year, going against earlier projections that would have put the low point in the past.

More than one out of every four homeowners is now underwater in their mortgage, meaning they owe more on their mortgage than their house is worth.

The report also discloses that one out of every thousand homes is now in foreclosure.

Foreclosures hit a three-year low in the first quarter, but filings are expected to jump 20 percent this year, real estate information service RealtyTrac said in January.