You are going to need to clarify or provide some details (such as bitcoin addresses and transactionIDs).
Are you saying that someone took the bitcoins from your MtGox account, or are you saying that someone took the bitcoins from a non-MtGox wallet?
I imiediatly purchased BTC with the USD and sent them to my wallet.
It looks like that person may be using adware/keygens/whatever to obtain mt gox passwords and taking their BTC.
Your MtGox password won't let them transfer bitcoins from a non-MtGox wallet.