Some Trojans can changes the bitcoin wallet adress to hacker wallet adress when you want to transfer your coins.
Example; following adress is dangerous. Be Carefull. Always update your antivirus program. And always double check adress before you transfer your coins.
This days Carefull about this adress:
https://blockchain.info/address/13AqmiwoRwR6grdFZSWQ1tDxDN9qkhwaPd