Also, the only one with access to my computer is the guy behind me, but he wouldn't do that. As for malware, I don't recall clicking any weird links
Not to rub salt in the wound, and just an honest question, but I don't understand why people keep large amounts of any coin on an exchange and not in a protected wallet. I guess the only thing I can see is if you are actively trading, but even then, it seems like the xfer fees and hassle are worth it seeing how relatively easy it is to steal coins. I hope Mintpal can help you out.
More than the tx fee, its the waiting for confirmtions in the exchanges that is a pain. You need to be quick if you want to trade in margins.... you cat do that with keeping coins in your wallet and spending the next half hour waiting for teh coins to get transferred. to top that off, BTC transaction speed is ridiculously slow.... and mintpal confirmations is the slowest!!