(Bloomberg News) Donald Johnson, a former managing director at the Nasdaq Stock Market, pleaded guilty to participating in an insider trading scheme, the U.S. Justice Department said in a statement.

Johnson, 56, pleaded guilty to one count of securities fraud, according to the statement today. He admitted he purchased and sold shares of Nasdaq-listed companies based on inside information on several occasions from 2006 to 2009, according to the statement.

"Mr. Johnson was a fox in a hen-house," Assistant Attorney General Lanny Breuer said in the statement. "Nasdaq-listed companies entrusted him with their sensitive, non-public information so that he could provide them with analyses about their stock. He then used that very information to cheat the system and make an illegal profit."

"We're fully cooperating with the authorities," said Frank De Maria, a spokesman for Nasdaq OMX, who declined to comment further.