The flash crash in 2010 gutted the stock market within minutes. The simple story recently revealed is that a trader placed lots of illegal sell orders hoping to drive down the price so he could buy back in cheaply. No grand conspiracy, but a small and critical flaw in the system. One defense is, if it happened so easily once, why hasn’t it happened more often. The answer is that it has; check DNDN from a few months earlier. The other answer is, more sophisticated variations may be more profitable, harder to detect, and far more pervasive than most expect. A concern, is that this simple exploit remained unexplained for years. Regulators can’t operate at the speed of the market they are supposed to regulate. The system is so vital to the global economy that it can’t be shut down while waiting for improvements. In the meantime, we continue, hoping nothing worse will happen – even though it may already be in progress.