A sufficiently capable quantum computer would break the public-key cryptography that secures most internet traffic. No such machine exists publicly. The disagreement is about when, and estimates span decades.
The reason it is not purely a future problem
Encrypted traffic can be captured now and decrypted later. If data must stay confidential for fifteen years, the relevant question is not whether the machine exists today but whether it will exist inside that window. For most commercial data, the answer is no and the urgency is low. For health records, state secrets and long-lived identity data, it is not.
What is worth doing now
- Know where your long-lived secrets are, and how long they must stay secret.
- Prefer libraries and protocols that support algorithm agility, so a swap is configuration rather than a rewrite.
- Adopt hybrid key exchange where your stack already supports it; the cost is small and the downside is bounded.
What can wait
Re-encrypting archives, replacing hardware security modules, and rebuilding systems around algorithms whose standards are still settling. Doing this early usually means doing it twice.