I think that the most dangerous attack in the upcoming years may be due to cyber attacks by using Quantum computers.It is said that quantum computers would be able to read the private keys of a bitcoin wallet with the public key itself.If that happens,then it would have a devastating effect over the bitcoin network.Its said that core developers are working from now itself to fix that issue.
Direct attacks on bitcoins will be very difficult because of their robustness and security. The attack is aimed only at e-wallets of investors or those who do not secure their assets. So they will attack and take away all your electronic money. Know how to protect your property so that you do not have to face unfortunate risks.