People have been talking about quantum computers threatening the cryptography used by Bitcoin, but here is an interesting article that is significantly less optimistic about the abilities of quantum computers.
It is a relatively short read and accessible to non quantum computer people.
For electronic qubits, the largest number factored is “21”, through a real quantum circuit of 4 qubits done in 2012: Computing prime factors with a Josephson phase qubit quantum processorFor photonic qubits, the record for the largest number factored is “15”, also with 4 qubits, done in 2007: Demonstration of Shor's quantum factoring algorithm using photonic qubitsThere has been zero progress since. Additionally, both these photonic and electronic qubit implementations of Shor's algorithm relied on prior knowledge of the factors. These demos used a compiled or semi-classical version of the algorithm, meaning they optimized the quantum circuit based on precomputed classical information about the solution. So, it essentially useless for computation, and was only meant to show ability of fine qubit control.