Account takeover (ATO) fraud happens when a bad actor gains control of someone's online account and uses it to steal money or personal data. In my experience at PuroClean, I've seen clues like unexpected password resets, unfamiliar login locations, or sudden changes to contact details. Criminals often harvest credentials from breaches and test them across financial sites. Banks, insurance, and fintech firms are especially at risk because of stored value and sensitive data. Prevention starts with strong MFA, regular password updates, and monitoring for unusual activity. Educating customers about phishing and device security helps reduce exposure. The key is combining technology with vigilant review.