Bernard L. Madoff, who helped start the Nasdaq Stock Market and has been a force in Wall Street trading for nearly 50 years, was arrested by federal a

Bernard L. Madoff, who helped start the Nasdaq Stock Market and has been a force in Wall Street trading for nearly 50 years, was arrested by federal agents Thursday, a day after allegedly telling two senior employees that his business was "a giant Ponzi scheme.The extent of investor losses alleged by federal prosecutors wasn't immediately clear, the alleged scheme involved the asset-management unit of Bernard L. Madoff Investment Securities LLC, a New York firm owned mostly by the 70-year-old Mr. Madoff.