I am suspicious of any claims that attribute the cause of this error to a software malfunction. I am fairly confident that the order was entered directly on Bloomberg. Not long ago, an erroneous market sell order was placed in NIHD for half a million shares on INCA. If my memory serves me correctly, on an instinet terminal, if you want to sell 100 shares, you type in 1. To sell 5000, you would enter 50. By incorrectly typing in 5000, a sell order for 500K would be generated. I don't know if instinet terminals are even in use anymore, but the gr8trade portal may have been engineered to accept order entry in the same way.
Never having traded from a Bloomberg terminal, I can't say for certain, but based on how antiquated the display looks, I'd guess that they operate the same way. I imagine an inexperienced trader at an institutional desk meant to sell 10K shares but instead of typing in 100, typed in 10000. Thus, the million shares that everyone saw. I believe this is why errors are usually a factor of 100. Anyone that trades from a Bloomberg, that can confirm or refute, your input is appreciated. Regardless of why the error happened, the fault should lie with the firm that entered the order. There is no reason that an alert shouldn't have been triggered, at the time of order entry and during the duration of the order. I can't conceive of a situation where it makes sense to legitimately display that much size on the bid or offer, unless it is one of the most liquid stocks, because it will certainly move the market unfavorably. The party that made the error is guilty of negligence at the very least, for not having a system in place that would prevent such ridiculous orders from being entered in the first place. Sadly, a deal was probably made with nasdaq, to accept a small fine in exchange for getting out of jail free.