At 7:04 a.m. on an autumn Thursday in Tokyo, the stewards of the world’s third-largest equity market realized they had a problem. A data device critical to the Tokyo Stock Exchange’s trading system had malfunctioned, and the automatic backup had failed to kick in. It was less than an hour before the system, called Arrowhead, was due to start processing orders in the $6 trillion equity market. Exchange officials could see no solution. "The full-day shutdown that ensued was the longest since the exchange switched to a fully electronic trading system in 1999". It drew criticism from market participants and authorities and shone a spotlight on a lesser-discussed vulnerability in the world’s financial plumbing -- not software or security risks but the danger when one of hundreds of pieces of hardware that make up a trading system decides to give up the ghost. That could lead to massive breakdown in just several minutes.