Integrity of the block chain

Thinking of Enigma, Ultra, Colossus, etc. I’m wondering if quantum computers could pose a threat to the integrity of the block chain?

probably within the next decade or two but I’m sure it will be pretty expensive at the start nonetheless cardano is developing protocols, check out this forum: Quantum Computing Updates .
In particular IOHK’s whitepapers: and and Research program to work on hardening Cardano against quantum computers - IOHK Blog