We already have a system subject to impersonation attacks and simple fraud. Major retailers and fiscal institutions both spend a considerable amount of time tracking fraud, and often catch it so easily that they need to wait until it accumulates to a point where it's worth reporting.

And, even if we were suddenly inundated with a level of fraud attempts sufficient to overwhelm the system, there is literally an entirely separate model of online finance that was designed to be zero trust.

And if "how existing banking" and "cryptocurrency" don't convince you we won't be reverting to cash, please realize that an AI ubiquitous to overwhelm global finance is also so ubiquitous that we might as well do what humans always actually do when commerce breaks down, and revert.to a gift economy.