Polymarket US was targeted in February 2026 by fraudsters who linked stolen debit cards to thousands of newly created accounts, placed wagers and attempted to withdraw proceeds to payment methods they controlled. The attempted flow totaled at least $10 million, though public reporting has not established how much money left the platform and a person familiar with the matter said most deposits failed. Checkout.com, Polymarket's debit-card processor, at one point classified more than 80% of deposits it handled for the platform as fraudulent, compared with an industry benchmark of about 1%. Seven users led the scheme, with one attempting more than 4,000 deposits, The Block reported. Checkout.com sought stricter controls after Visa issued a warning, according to the report. Compliance staff escalated the attack to Chief Executive Officer Shayne Coplan, who was reported to have prioritized growth despite the risks. Polymarket later removed a same-source withdrawal control intended to require funds to return to the payment method used for a deposit, despite employee concerns that the change could facilitate money laundering. Fraud rates remained elevated for months before nearing industry norms by May after the company restricted the number of debit cards linked to an account and hired Riskified. The episode was followed by the resignation of Polymarket US Chief Compliance Officer Andrew Clifford, the dismissal of U.S. division CEO Justin Hertzberg and departures by the heads of American regulation and Anti-Money Laundering. The CFTC is investigating the company, while the New York City Council, traders and state plaintiffs have separately raised concerns about its advertising and operations. Polymarket says it has strengthened its risk controls, added staff and remains committed to working with regulators and law enforcement. The compliance scrutiny comes as Coplan seeks roughly $1 billion at an approximately $21 billion valuation. Donald Trump Jr.'s 1789 Capital is contributing about $300 million to the round, while Intercontinental Exchange invested $600 million in March, according to later capital-markets reporting. Polymarket appointed Warren Jenson as its first chief financial officer in September as it prepares operations for a possible 2027 listing.