Hacking Bitcoin is completely impossible. But still, hackers have shown that this can also be done. The most prominent hacking history of Bitcoin was that of the Japenese Bitcoin Mt Gox in summer of 2014. It was the largest Bitcoin exchange at that time and was operating since 2010.
So Bitcoin hacking has increased recently. Bitcoin hacking has occurred through the companies that do some kind of fundraising they ask people to donate to them and hence their data are leaked. This happens because when people buy Bitcoin they have some kind of private key to the blockchain. The hackers sometimes pretend to be these companies and loot people out of their money so people must be very conscious about which the real companies are and which ones are the fake ones.
Even though hacking incidents have increased the security involving the security of the owners have also improved. Bitcoin can never be hacked as it is believed so. The Bitcoin provides private keys to every owner and the security to these keys is anyway compromised than the Bitcoin users is moved to another address. Moreover, Bitcoin is never controlled by any person or organization. There is no doubt that the hackers make repeated efforts to hack the Bitcoin system but there are mechanisms that prevent the system from any attacks. In fact, every cryptocurrency is secured with such mechanisms and every one of them is quite safe and secure.
Large cryptocurrencies are somewhat protected from hackers as the hackers do not have much of an incentive frauding such large cryptocurrencies like Bitcoin, ethereum, etc. because they could instead mine such large cryptocurrencies and earn enough rather than spend the efforts in cheating them.
None the fewer hackers apply petty techniques like advertisements and fraud companies to cheat and if the owners are smart and aware enough they can easily prevent themselves from being cheated.