Five facts explain what quantum computers change, what they do not, and why

Superposition does not let quantum computers test every answer by brute force, because measurement reveals only limited information.

Today’s quantum computers are rudimentary and error-prone, while most proposed applications may be years or decades away.

A future capable quantum computer could threaten some current encryption, but nobody knows when it will appear.

Post-quantum cryptography uses encryption and signatures designed to resist conventional and quantum computers, so migration should start now.