Yes. In 99% of cases it is illegal. There are some cases when it ok to keep it (like if one pays off their loan too early [1]) but you will be criminally prosec

Yes. In 99% of cases it is illegal. There are some cases when it ok to keep it (like if one pays off their loan too early [1]) but you will be criminally prosecuted if you do not return money you have no reason to believe it should be yours [2]. [1] https://www.cnn.com/2021/02/16/business/citibank-revlon-lawsuit-ruling/index.html https://www.cnn.com/2021/02/16/business/citibank-revlon-laws... [2] https://www.ktvu.com/news/woman-jailed-after-refusing-to-return-1-2-million-mistakenly-put-into-her-bank-account https://www.ktvu.com/news/woman-jailed-after-refusing-to-ret...