If you have $5000 in a bank account, and a bug in the bank UI lets you withdraw $10000, the bank can and will come after you to get their money back. And if you intentionally exploit this bug to create 100 accounts with $5000 and withdraw a million, you've definitely committed a crime.

I once had money deposited in to my account, repeatedly, that wasn't mine. It was a pain in the ass. I didn't want it.

I asked my gf's dad, a lawyer, if I could spend it. He said no: it's like someone parking their car on your driveway. It's annoying, sure. But it doesn't make it your car.

>Just keep stacking it in a savings account and collect the interest. If you wanted to take some risk you could also invest some of it in index funds.

A friend of mine is addressing a similar situation right now. After her mother passed away (nearly 20 years ago) and left no will, her primary bank account was still active and the Social Security Administration[0] kept sending her checks every month.

She was notified a few weeks ago of the existence of this account (which now has several hundred thousand dollars in it). Since Social Security benefits (except in specific circumstances[1]) are not collectible by surviving relatives, the moneys paid into that account since her mother's death are not hers (she and her siblings are the only surviving next-of-kin). Rather those funds are the property of the US Government.

In such a circumstance, the funds deposited, as well as any interest on those funds belong to the government.

Transferring those funds or spending any of the interest is a crime.

As such, if you find yourself in a similar situation, I'd think twice before doing something like that.

[0] https://www.ssa.gov/

[1] https://www.cnbc.com/2021/08/16/heres-what-happens-to-social...

And if the bank says “how did you do that?”, you explain and they thank you, let you keep the money and also give you a reward, then what?

Then why isn't it illegal for a bank to make an error and keep _your_ money if the reverse is never going to be allowed to happen?

> Then why isn’t it illegal for a bank to make an error and keep _your_ money if the reverse is never going to be allowed to happen?

It… is.

The difference is that the bank (1) is often in a better position to automatically recover funds from you when they discover an error than vice-versa, (2) has better resources for collection via civil process if they aren’t in a position to automatically recover funds, and (3) has better connections with law enforcement to use if there is any indication of a criminal exploit.