Polymarket US faced an attempted fraud scheme involving at least $10 million in stolen debit-card transactions earlier this year as the prediction-market company pushed to expand its regulated U.S. business. Fraudsters linked stolen cards to thousands of Polymarket US accounts in February, deposited funds and attempted to move the money through wagers before withdrawing it to cards or accounts they controlled. At one point, payment processor Checkout.com rejected more than 80% of deposits it handled as fraudulent, compared with an industry rate of roughly 1%.