More than 100 of the largest banks and securities firms in the world have incurred more than $500 billion in write-downs and credit losses as problems spread to other asset types. "It just keeps spreading from one asset to another, so it's hard to know when these write-downs will stop," said analyst Makeem Asif of KBC Financial Products in London. "The U.S. economy needs to stabilize first. But even then, Europe could lag and recover later. There's still a lot more downside."