You have no idea what you are talking about, clearly.
CDS - I'm sure refers to Credit-Default Swap, essentially an insurance policy purchased by an investor from an insurance company (mainly AIG) to secure revenues from a CDO
Banks do not Cover CDS as they are an insurance product, not a banking product.
CDO = Collateralized Debt Obligation. An asset backed security also does not need to be backed by banks, as it is an investment sold to investors. Essentially a bundle of Mortgages sliced into risk categories and sold for different amounts offering revenue streams at varying levels of risk. The Sale of CDO's recapitalize banks allowing them to make more loans. It is the holdings of these investments that carries the risk, the holding of Mortgages themselves carry the same risk. So, Banks reduce their risk by selling CDO's or MBS', whatever you'd prefer to call them, and the investors who adopt that risk in exchange for the collective profits of their constituent mortgages.
Please, stop trying to to act like you know what you are talking about.