It stands to be a big question mark until 2009

Mortgage securities typically consist of 10 or more different slices -- from highly rated slices for conservative investors all the way down to low-rated, riskier slices for investorslooking for bigger returns.

Each slice has its own set of rules governing when and how investors will get paid or suffer losses.

Rising defaults can actually be good for some highly rated slices, which get paid off faster as a result.

Many lower-rated slices, though, pay back the original investment only after three years, and only on the condition that defaults remain low.

That means the value of a security issued in 2006 stands to be a big question mark until 2009.