Mortgage banks kept some claims on their books, but sold most of them to investment banks as “mortgage-backed securities.” The investment banks blended these securities into “asset-backed securities” and “collateralized debt obligations” (CDOs) and sold them on to financial institutions throughout the world.
这一危机的蔓延，是因为银行系统避险性不够-在某些情况下它甚至偏爱风险。抵押贷款银行把一些未收的资金放在帐簿上，但把其中的大部分以“以抵押为后盾的证券”售给投资银行。这些投资银行又把这些证券混合为“以资产为后盾的证券”和抵押债务契约（ CDOs ）出售给世界各地的金融机构。这些机构被高回报率的所吸引，而总是忽视了下行风险