http://www.latimes.com/business/la-fi-nikkei14dec14,...
"After initially denying any responsibility for the J-Com snafu, exchange executives acknowledged this week that flaws in their electronic trading system prevented Mizuho from correcting its order and minimizing losses. Mizuho traders realized their mistake within 85 seconds of placing the erroneous order and made four attempts to cancel it. It was rejected each time"