If that doesn't make sense then, we have three options left:
1) The REAL Account Owner: The hacked account "single user" account are Mt.Gox's or it belongs to someone closely related to Mt.Gox.
2) The PWNAGE Cover Up:The "single user account" is a cover story to hide the fact that actually the site got compromised much deeper than they are willing to admit. (loss of credibility would be the death of Mt.Gox)[/size]
Bingo.
My guess is that it was their 'bank' account or something to that effect which actually contained the total funds in BTC of the entire exchange or a sizable portion of it. I'm about 90% certain that they are insolvent and probably shitting bricks right now trying to determine what to do about it. It might not be up for quite a while. If they are insolvent that raises an interesting question:
1) Is it a 'bank run' as soon as the exchange opens? (expect X lawsuits)
2) Do all MtGox assets get triaged and we get a portion of what we held there? (expect 10x lawsuits)
3) Does and can MtGox "eat" the loses and then pays to make everyone whole (definitely the best long term solution for them),but do they have the assets?
a. If they don't can they raise money to buy BTC over-the-counter to become re-solvent? Or do they come clean about insolvency and not allow people to withdraw until they gain enough money in fees to make everyone whole. (this would crush the price of BTC into the ground but probably have the least legal implications).
b. Remain insolvent, don't tell this and hope that there isn't a 'bank run' (hopefully nobody over there at MtGox is proposing this, this is a BAD idea)
On a side note should the Exchanges prevent this type of 'dumping'? I would definitely say yes that a certain account can only sell so much at least making the user have to have multiple accounts in order to dump more, therefore lowering the security risk by having a single user with 500k BTC, if you buy that story.
Lol, I bet the 'free market' fanatics here are starting to see how regulation comes into existence.