I've seen this story (NASDAQ being hacked) reported in a couple of places, but it isn't clear to me what damage was done. It's not really possible for them to have messed with the actual trading without anyone noticing. Everyone connecting to an exchange is reconciling the orders they send in against the trade confirmations they receive. You basically design your technology assuming the exchange is going to fuck something up eventually. I'd really like to hear more details about what was going on here.