Charges filed by the Justice Department last week accuse two former brokers at the New York office of Linkbrokers Derivatives, Marek Leszczynski and Benjamin Chouchane, of securities fraud and conspiracy for secretly adding a few pennies to the cost of securities trades processed by the firm to generate $18.7 million in gains, the New York Times DealBook blog reported yesterday. A sales trader and middle-office assistant at the firm, Henry A. Condron, entered a guilty plea and is cooperating in the government's case. The Securities and Exchange Commission also filed civil charges against the three men, and added another broker as a defendant who was not named in the criminal case.