N.B: I have my bitcoin address of my last transaction so I need the private key of this address.
Thanks !
That is just impossible to get it back. There is no way you can make this hack happen and get your bitcoins back. There is only one way to do it and thats by getting your private keys. The way to get them is to look for the place where you stored it, may be email, key logger, pasted in the notebook or something like that. You have to stress yourself to remember where you might have stored it. So get that key and then we ca talk about the hack. The hack is not possible in the bitcoin wallet and that is how it is designed in the first place. The security is so much that not even the wallet provider can do anything about it.