As a Trust & Safety Manager at Wallapop, the leading classified marketplace in Spain, I have the privilege of contributing to the platform’s mission of connecting over 15 million people through an easy and convenient way to buy and sell items. My role involves ensuring that Wallapop’s community remains safe and trustworthy by implementing and enforcing policies and procedures that promote ethical behavior and discourage fraudulent activities. I want to share our learnings from the unprecedented challenge we faced last year. We noticed an increase in account takeovers, but a new kind: account takeovers without any logins. For more than three months, we tried every trick in the book but were unable to find the root cause of the issue. During the talk, I want to discuss the lessons we learned about the importance of perseverance, innovation, and finding new ways to understand fraud. I will also share what our team would have done differently and provide valuable security tips for the attendees.