Software Engineering View of a Large-Scale System Failure and the Following Lawsuit

In 2005, a system trouble occurred in the Tokyo Stock Exchange Order System, which caused a loss of more than 40 billion yen to Mizuho Securities and Mizuho filed a lawsuit demanding compensation for the loss to the Tokyo Stock Exchange (TSE). The judgment was pronounced in December 2009, ordering TSE to pay Mizuho Securities about 10 billion yen in compensation for the loss. Mizuho Securities found the judgment unacceptable and appealed to the Tokyo High Court. The judgment of the appellate court was issued in July 2013, basically upholding the initial verdict. From the software engineering point of view, the most important incident during the appellate court was partial disclosure of the source code of the system. We report the incident from the viewpoint of software engineering, making use of the partially disclosed source code. We discuss various issues, focusing on the role of SE searchers and engineers.