The dastardly deeds of the credit default swap.

Listen to an audio podcast of this article by clicking the arrow on the audio player below:

When you hear that the collapse of AIG or Lehman Bros. or Bear Stearns might lead to a systemic collapse of the global financial system, the feared culprit is, largely, that once-obscure (OK, still obscure) instrument known as a credit default swap.

So, what is a CDS, and why is it so dangerous?

At first glance, a credit default swap seems like a perfectly sensible financial tool. It is, basically, insurance on bonds. Imagine a large bank buys some bonds issued by General Electric. The bank expects to receive a steady stream of payments from GE over the years. That's how bonds work: The issuer pays the bondholder some money every six months. But the bank figures there's a chance that GE might go bankrupt. It's a small chance, but not zero, and if it happens, the bank doesn't get any more of those payments.

The bank might decide to buy a CDS, a sort of insurance policy. If GE never goes bankrupt, the bank is out whatever premium it paid for the CDS. If GE goes bankrupt and stops paying its bondholders, the bank gets money from whoever sold the CDS.