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A fat finger error is a widely used term in the finance industry and describes a typographical error supposedly caused by hitting the wrong key, or by making mistakes when inputting a quantity into a computer (for example, adding a zero to the end of a figure).
Since the advent of trading on computers, errors involving so-called "fat fingers" have rarely been far away. Among the most notable examples came in 2006 when an error by a trader at Mizuho Securities in Japan left the broker with a large short position that it had to unwind at a cost of more than Y40bn. More recently a sudden 15 per cent drop in the value of Mumbai stock exchange was caused by a fat finger. However the emergence of high-frequency trading, in which buy and sell signals for assets are often taken automatically from trades made by computers, has blurred the lines between human, "fat finger" errors and computer-driven trades. Increasingly, exchanges and brokers have been developing operational and technological safeguards such as "kill switches" to limit damage from errant trading. In January 2013 some sources were blaming "fat finger errors" for some hard to fathom Euribor quotes from banks.