The chances of stealing bitcoin in the way you thought is quite impossible or maybe just not too possible to happen. Bitcoin would not have been trusted by millions of people if your idea works. Of course, people would always do something to be evil in some ways but stealing through that method could lead them to a dead end. The security system that was created for Bitcoin could be considered steal-proof because Bitcoin is used for all kinds of transactions; good and bad. So do not be worried about your coins being stolen because they made sure your coins are safe.