A former Nasdaq managing director was sentenced Friday to 42 months in prison for insider trading, the Justice Department said.Donald Johnson pleaded guilty in May to one count of securities fraud, admitting he used inside information obtained through his position as an executive at the stock exchange operator that netted him $755,066 in illicit profits. Johnson, 57, was sentenced by a US federal judge in Virginia and also ordered to give up the $755,066 in illicit profits he had pocketed, the Justice Department said in a statement. \"Today\'s sentence should leave no doubt in the minds of investors inclined to cheat that insider trading is a serious crime, with serious consequences,\" said Lanny Breuer, assistant attorney general of the Justice Department\'s criminal division. Johnson had been a managing director on the tech-rich Nasdaq\'s market intelligence desk in New York when he engaged in insider trading between 2006 and 2009. According to authorities, Johnson frequently placed the illegal trades directly from his work computer through an online brokerage account in the name of his wife, Dalila Lopez. Johnson admitted he made the illegal trades on at least eight different occasions. The companies whose securities he traded illegally were Central Garden and Pet Co.; Digene Corporation; Idexx Laboratories Inc.; Pharmaceutical Product Development Inc.; and United Therapeutics Corporation.The markets regulator, the Securities and Exchange Commission, has filed a related civil enforcement action against Johnson in New York.