...are actually worth a negative amount since they cost money and should be considered a liability, not an asset. Say the underlying assets are mortgages secured to houses. Most are in default while the rest have been foreclosed upon so no money is coming in at all. Yet there is costs that have to be paid. The eviction process is a major one time cost, but then there is property taxes that still must be paid and sky high insurance rates on vacant property. Not to mention general maintenance required by the municipality such as lawn care. They cannot be sold without a major mark down of the price with the banks are not prepared to make, but are being bleed to the the carrying costs of all these vacant homes with may be thousands per year per house. So what was once considered an asset with positive cash flow is now a liability with negative cash flow. Just my two cents...