Mizuho Securities 'fat-finger' J-Com order error
A trader's mistyped sell order and the Tokyo Stock Exchange's own system bugs combined to cost Mizuho Securities roughly $340 million in a single botched trade.
The damage was public. The root cause was preventable.
A trader's mistyped sell order and the Tokyo Stock Exchange's own system bugs combined to cost Mizuho Securities roughly $340 million in a single botched trade.
What the software actually got wrong
A Mizuho trader meant to sell 1 share of J-Com stock for 600,000 yen but instead entered an order to sell 600,000 shares for 1 yen each; when Mizuho tried to cancel the erroneous order, a bug in the Tokyo Stock Exchange's trading system prevented the cancellation from going through in time, letting the order execute in full.
A Mizuho trader meant to sell 1 share of...
A Mizuho trader meant to sell 1 share of J-Com stock for 600,000 yen but instead entered an order to sell 600,000 shares for 1 yen each
Requs AI Edge Case flags this exact pattern at the requirements and architecture stage — before a single line of code implementing it exists — so the assumption behind it gets challenged while it is still cheap to fix.
When Mizuho tried to cancel the erroneous order, a...
when Mizuho tried to cancel the erroneous order, a bug in the Tokyo Stock Exchange's trading system prevented the cancellation from going through in time, letting the order execute in full
Requs AI Software FMEA traces this failure mode back to the system-level hazard it feeds, tagging it against the Common Defect Enumeration so it surfaces in review instead of in the field.
Beyond code coverage and "shall" testing
Root causes like this one rarely show up in code coverage or requirements-compliance testing, because nobody wrote a requirement anticipating the specific edge case that broke. Requs AI Edge Case and Requs AI Software FMEA are built to surface exactly this class of overlooked failure mode — before the software is written.
Surfaces this before code exists
Identifies edge cases like this one at requirements and architecture time, using the Common Defect Enumeration to catalog failure patterns seen across hundreds of real-world software failures — including this one.
Connects the failure mode to the hazard
Traces this class of root cause directly to the system-level hazard it can produce, so a defect pattern like this one gets flagged during design review instead of after it ships.
Find the overlooked root causes before they ship.
Schedule a demonstration, or explore how Requs AI Edge Case and Software FMEA use the Common Defect Enumeration.