In fact, Bitcoin is theoretically vulnerable to hacking due to its code is open source and programmer can be constantly reviewing it. There is one type of hacking which can successfully hacked bitcoin which called the 51 percent attack. Due to bitcoin is decentralized, bitcoin will be vulnerable if more than 50 percent of the computing power is being controlled by any one of the player. There is one case where a group of people has achieved control 50 percent of the bitcoin network's power. However, hacking bitcoin is not that easy. When you are controlling such huge percentage of the power, you computer must be really good and the electricity bill can be very high. And also the more the poeple using bitcoin, the larger the network, the harder for the people to hack in.