I haven't been following this terribly closely but, the seemed to recognize the problem almost immediately, they warned their customers that there might be a problem. I can't explain what they did yesterday but I am sure they are much closer to the SEC and most likely were being advised that this might have to all unwound somehow. Not to mention talking to their own legal department. I think they are obligated if they know there is a problem to stop trading in the stock. The fact that they did not notify you might be simply because they were busy trying to find and halt the trading in the stock.
Now, what about all the people who bought the stock knowing that it was being sold in the first place do to an error, what are the ethics there? In the first place it was either error or fraud, which one are they taking advantage of and why are they passing it on?
One other thing for the people who are saying this won't cost them, it will cost them a lot of money. Time, fees, legal advise, maybe even a few court cases.
Market Data 
Markets 
AI
