Prediction market Polymarket halted trading on its international platform on Oct. 29 after users reported unauthorized withdrawals from their wallets. The company said the breach stemmed from a compromised third-party vendor.
Polymarket blocked new orders and trades, allowing only cancellations of existing ones, and paused relayer actions while it investigated. “One of our third party providers was compromised, and we have referred this to relevant law enforcement,” the company said.
Blockchain analytics firm Arkham traced the attacker swapping stolen funds from USDC.e into POL tokens through the Relay service and moving them to other wallets, putting total outflows at $2.65 million. Tracker DeFiLlama put the losses at about $2.7 million. Trading resumed the same day, and Polymarket pledged to fully reimburse affected traders but gave no specific timeline for payouts.
A compromised vendor serving the platform's frontend already cost Polymarket users about $3 million in a breach in June 2026.
