
...
Bitcoin.com News (BCN): What are quantum computing attacks, and what threat do they pose to blockchains and cryptocurrencies? How long will it be before quantum computers are capable of breaking the security algorithms in blockchains?
Johann Polecsak (JP): Powerful quantum computers with sufficient stable qubits will be able to break today’s cybersecurity standards. Today’s asymmetric cryptographic algorithms like RSA and EC used by the whole internet – including governments, banks, email providers, social media, blockchain platforms, etc .– will be cracked by quantum computers.
This threat affects blockchain technology as follows: all cryptocurrency wallets relying on Elliptic Curve (EC) cryptography which have at least one outgoing transaction will break. In short: hackers will be able to steal your cryptocurrency.
We are already having the wrong conversation in cryptography if we argue about whether we have 1, 3, or 5 years before quantum computers will break today’s security algorithms. We must always be ahead of the curve when it comes to cybersecurity.
...
More:

Existing Blockchains Can’t Adopt Post-Quantum Cryptography Without Significant User Impact, Says Johann Polecsak – Interview Bitcoin News
Polecsak suggested that Google’s quantum computing breakthrough in 2019 should serve as a wake-up call to enterprises and governments.
I thought that was an interesting interview. Johann is of course touting his own quantum resistant crypto, so there is an element of salesmanship happening. I seem to remember skimming though a technical paper some weeks or months ago where developers for another blockchain were talking about upgrades that would be quantum computing resistant, but I didn't make a note of it. I suspect that this issue will develop over time, so I'll be sure to post relevant updates here as I find them.