Federal regulators are investigating MF Global after discovering that hundreds of millions of dollars in customers' money has gone missing in recent days. Initially, close to $1 billion was said to be missing, but the figure was revised to less than $700 million by late Monday. The company filed for bankruptcy-court protection on Monday, and investigators are checking whether MF Global attempted to use customers' money to support its own trades. News of the missing money derailed the company’s last-ditch effort to sell a major part of itself to a competing brokerage firm. MF Global has not yet been accused of any wrongdoing.