There is one type of attack that could affect the bitcoin network: the 51 percent attack, which is widely considered to be bitcoin’s greatest inherent flaw. Because it is decentralized, bitcoin is vulnerable if any one player or cartel gains control of 51 percent of the computing power of all miners. This would allow them to stop transactions and reverse transactions, which would throw the network into chaos. In the past, at least one group has achieved control of 50 percent of the network. However, the more people using bitcoin, the safer it is — and more people are using bitcoin now than ever. It’s difficult to get an accurate count of how many users bitcoin has, but the estimates are in the millions.
Where Bitcoin becomes truly insecure is when other technology starts to get involved. Bitcoin was conceived as a “trustless” system; you don’t have to trust any centralized party in order to use your money, because transactions are facilitated by other members of the network. In reality, bitcoin is too complicated for most people to use without mediators such as apps, wallets, and other digital currency services. The biggest need is for third party exchanges, which are sites where bitcoin is bought and sold for other currencies. All these third party services are only as safe as their own security. Mt. Gox, arguably the most famous example of an exchange going belly up, filed for bankruptcy in early 2014 after around 850,000 bitcoins went missing.
Bitcoin is still largely unregulated, which means your money isn’t insured and there is often no accountability for exchanges. So while bitcoin tech itself remains unhacked, the methods used to collect, buy, and sell remain as potential attack vectors.