I hear this term all the time on the news and since many of you seem to know what you are talking about, what is a toxic asset and why are they such a big deal?
Well a toxic asset can really be a simple mortgage as I described above, but this current mess does have a lot of what you are referring to, which are more commonly called CDOs or "collateralized debt obligations." These are basically just assets made by splitting up mortgages and repackaging them, so that each CDO had bits and pieces of thousands of mortgages in it. It was a good way to invest in large parts of the market at once and it was basically a bet on the market going up as a whole. Sadly a lot of the people who created these CDOs did think the market would continue to go up forever and a lot of the people who bought them either agreed or didn't even understand what CDOs were. Obviously the market went down and when mortgages started going toxic, we were left with an even messier situation because so many of them had been split up and repacked into these CDOs.I think the really toxic assets are the derivitives and swaps that are either so complex that it literally takes a PhD in Mathematics to understand them or that are based on outrageous false assumptions, like the idea that the housing market will never have a downtrend.