Banks typically make errors in their favor, but occasionally, an error is made in your favor. But that doesn't mean you can profit from it. The bank has the right to take the money back anytime in the future.FiveCentNickel described
a case in which his bank mistakenly made an extra deposit into his account. He has notified the bank of the mistake and will be keeping the money in the account while he waits for the bank to correct the mistake. That's probably the best way to handle it.