>I am interested to know if the stop command was a "save your own skin" move or a "save the market" safeguard. Definitely "save your own skin." The consequence

>I am interested to know if the stop command was a "save your own skin" move or a "save the market" safeguard. Definitely "save your own skin." The consequences can be dire when trades are "busted" (as many were). Consider this hypothetical situation: Shares of a stock are trading at $50. After that plunge on Thursday, it's trading at $18, and an algorithm jumps in. The shares rally and at $22, the algorithm sells the shares for a quick profit, and calls it a day. The shares go back to $45 by the end of the day. (This is basically what happened). The next day, NASDAQ rules that all trades at a price below 40% of the price before the plunge [are invalid](http://www.streetinsider.com/Insiders+Blog/NASDAQ+Busts+A+Number+of+Trades,+But+Says+Its+System+Ran+Problem-Free+During+the+Crash/5607699.html http://www.streetinsider.com/Insiders+Blog/NASDAQ+Busts+A+Nu...). Now that purchase at $18 didn't happen, but the sale at $22 did, and the high frequency trader is short the stock at $22, with the current price $45. That's why lots of high frequency trading shops shut down when trades are in danger of being busted. Note: I don't do high frequency trading, this was just from interested reading after that plunge happened last Thursday. It seems bizarre to me that they can rule a purchase invalid but keep the sale, but I believe that's what happens.