http://finance.fortune.cnn.com/2012...eed:+rss/magazines_fortune+(Fortune+Magazine)
""On Wednesday, the same day that Knight lost $440 million, the NYSE launched its own computer driven trading system, called the Retail Liquidity Program, that the exchange hopes will reclaim some of the trading volume it has lost to market makers. Like Knight, the NYSE's RLP computers use algorithms to figure out when it makes sense to offer a slightly better price than what others are offering, and snatch up stock trades, this time away from Knight and others.
Knight says the computer problems it ran into had to do with NYSE's new trading system, but it didn't say what. Tellingly, all of the stocks that Knight's computers did bogus trades in were listed on the NYSE. It's likely that Knight tried to upgrade its own algorithm to allow its computers to do an end around the NYSE's new system. But it messed up somehow. Instead, Knight's computer system, launched at the same time as the NYSE's, went on a trading frenzy, buying and selling millions of shares for no reason shortly after both systems were switched on, at when the market opened at 9:30 Wednesday morning.
Normally that shouldn't have produced any real losses. These weren't actual orders, so Knight's system should have just been buying and selling to itself. But that's not how the world of high frequency trading works. When other traders, i.e. computer systems, saw the spike in activity, they jumped in too."""