"Credit default swaps are a type of credit insurance contract in which one party pays another party to protect it from the risk of default on a particular debt instrument. If that debt instrument (a bond, a bank loan, a mortgage) defaults, the insurer compensates the insured for his loss. The insurer (which could be a bank, an investment bank or a hedge fund) is required to post collateral to support its payment obligation, but in the insane credit environment that preceded the credit crisis, this collateral deposit was generally too small. As a result, the credit default market is best described as an insurance market where many of the individual trades are undercapitalized."
Swaps proved to be very profitable — in the short term. Banks and other companies that issued them earned fees for insuring events they thought would never happen, like the bottom falling out of the market for mortgage-backed securities. As a result, the losses produced by the end of the housing bubble were multiplied manyfold, as the issuers of swaps found themselves faced with huge liabilities they had not prepared for. It was this cycle that brought down the American International Group, the insurance giant, which eventually needed $180 billion in taxpayer support.
Credit Default Swaps - The New York Times
Come back and dance ANYTIME.
Mortgage backed securities tanked, which tanked the default credit swaps, which the greeks bought in droves.
So yeah, if you like, we can chalk up the financial disaster in Greece to US CONZ (Specifically Phil "Foreclosure" Gramm) who deregulated these shitty financial instruments into legality.