The data entry error that cost hundreds of millions

cautionary tales
The mechanics behind a significant trading error at Mizuho Securities in Japan on December 8th, 2005, where a trader swapped the quantity and price leading to instant profit for others who bought the cheaply priced stock.

Lucas A. Meyer


December 8, 2022

Have you ever had a bad day at work? On December 8th, 2005, a trader at Mizuho Securities in Japan probably had a worse one.

That Thursday, a trader wanted to sell one share of J-Com for 610,000 yen (back then, this was about $3,600). However, when placing the order, they swapped the quantity and price, and ended up offering to sell 610,000 shares for 1 yen each. The company tried to cancel the order on the Tokyo Stock Exchange unsuccessfuly. People scooped the cheaply priced stock and resold it for instant profit.

The next day, the president of Mizuho said in a press release: “Someone unintentionally ignored the alerts.” It’s a good sign that there were alerts.

Every December 8th, I raise a glass to that unnamed trader and count my blessings.