The fundamental rules of the protocol and cryptography of bitcoin are very strong and it would take so much effort to hack. which security system has been improved over time in various software implementation. The technology of blockchain behind it is what makes bitcoin very difficult to penetrate.
So far Bitcoin itself has never been hacked. People always confuse Bitcoin hacked to cryptocurrency exchange or online wallet hacked. Exchanges and online wallets have various security risk as its connected to the internet. However, over the past few years, several security features have been added in exchanges and online wallets such as wallet encryption, multi-signature transactions, and much more.
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