Fraudsters attempted to steal at least $10 million from Polymarket's US prediction-market platform in February by funding accounts with stolen debit cards, placing bets and attempting to withdraw proceeds elsewhere, The Wall Street Journal reported. Checkout.com rejected more than 80% of the Polymarket US deposits it handled as fraudulent at the height of the attack, versus roughly 1% normally. The Journal reported that CEO Shayne Coplan urged staff to prioritize growth despite regulatory concerns and that the company loosened a withdrawal safeguard over employee warnings of increased money-laundering risk. US compliance chief Andrew Clifford resigned in April after submitting a report on the fraud issues. Polymarket said it is scaling responsibly through leadership hires and infrastructure upgrades, while Sullivan & Cromwell concluded it complied with applicable regulations. The CFTC has neither confirmed nor denied that it is investigating the company. The allegations come as Intercontinental Exchange invested $1.6 billion in Polymarket, which was valued at $21 billion in a $1 billion funding round led by Donald Trump Jr.'s 1789 Capital. Separately, unusual volume patterns in Kalshi's Ethereum perpetual futures market have drawn scrutiny, while Robinhood's event-contract revenue rose to $156 million in the second quarter.