Comment by iraklism

We deal with this almost every week, as in, we get into systems by searching through email:password leaks and use them.

There are a number of mitigating controls that can be applied here. Most will hamper usability, some will not.

There is a “simple” solution. Enforce 2FA. If not at the login, then before “dangerous” actions (transfer funds , change password , buy X/Y/Z )