Now that the White House has declared swine flu a national emergency, and with the H1N1 vaccine in short supply, many Web sites have been peddling swine flu nostrums. The Food and Drug Administration has identified 140 different dubious products sold online and has sent letters to 75 manufacturers. It is violation of federal law to market products that claim to prevent or treat H1N1 and that have not been approved by the FDA. The agency has gone after sellers of gloves, inhalers, masks, shampoos, herbal extracts, air fresheners, and an array of vitamins that make claims about fighting swine flu. Some of the Web sites were fly-by-night operations that have since closed down.