Many bitcoin exchanges allow users to store two balances: one in bitcoin and one in a fiat currency like USD. This is convenient because it allows one to trade in and out of the bitcoin market without incurring the fees and delays of moving money in and out of the exchange.
There have been numerous cases of theft from bitcoin exchanges, but have any of them lost users' fiat funds stored in this way? Or have only bitcoin balances been depleted by thieves?
Have any of the major exchanges made any statements (please link!) about how secure a user's fiat currency stored by them is?