The US Securities and Exchange Commission recently launched a formal investigation into possible insider trading at the Cambridge, Mass.-based biotechnology firm Biogen Idec. In March, Thomas Bucknum, the company's chief counsel, resigned following reports that he had sold stock in the firm just as potential safety problems with the multiple sclerosis drug Tysabri were coming to light. When those safety problems were made public in February, the drug was withdrawn from the market and Biogen's stock plummeted more than 40% in a single day.