I don't know how dangerous a quantum computer is, but I know how dangerous, even now, artificial intelligence, a system that supports password guessing!
Cybercriminals use artificial intelligence and neural networks to improve user password guessing algorithms. More traditional approaches, such as HashCat and John the Ripper, already exist and compare different variants of the password hash to successfully identify the password that matches the hash. However, using neural networks and Generative Adversarial Networks (GAN), cybercriminals will be able to analyze vast sets of password data and generate password variations that match a statistical distribution. In the future, this will lead to more accurate and targeted guessing of passwords and a higher chance of profit.

In a February 2020 clandestine forum post, we found a GitHub repository that has a password analysis tool with the ability to parse 1.4 billion accounts and generate password variation rules.
In addition, we also saw a post listing a collection of open-source hacking tools that have been cracked. Among these tools is AI-based software that can analyze a large set of password data from data leaks. This software ensures that it extends its ability to guess passwords by teaching GAN how people tend to change and update passwords.