The Federal Trade Commission and other federal authorities are now aggressively investigating Internet credit card fraud scams following a brazen attempt by cyberthiefs to extract personal card data from America Online’s 8.5 million subscribers. Earlier this month AOL subscribers received an official-looking, but bogus e-mail, which featured a letter from AOL’s chief executive, informing the recipient to supply address, phone number and credit card info to update AOL’s files. Federal investigators indicated yesterday such scams have spread beyond online services to Web sites offering bogus credit card offers or other on-line financial products.