Quantum computing could be used to reduce the difficulty of hashing by around 1/5th (Quantum computing reduces the number of bits needed for computations due to the fact that a qubit can assume a state of both zero and one at the same time.)
I was worried that one day this powerful quantum computer can hack private keys in seconds. According the text, quantum computing can reduce difficulty by only a fifth. So when they can actually build a usable quantum computer, security is at risk, not totally ineffective.
Quantum Computing is not exactly upgrade over normal technology, people don't understand that quantum technology is not giant leap forward and our processing power will be over 9000 all of a sudden. The problem with quantum computing is that result of the calculations of quantum based compter is not 100% correct all the time, and therefore quantum computer is not the best tool to crack passwords and encryptions.