Polymarket, a prediction market platform on the Polygon blockchain, has suffered a $700,000 loss due to a compromised private key dating back six years. The breach, which affected the platform's internal rewards wallet, did not impact user deposits or market outcomes. On-chain investigators ZachXBT and Bubblemaps first identified the suspicious activity on May 22, with the attacker moving funds through multiple addresses, exchanges, and mixers. The compromised wallet was used for distributing user engagement rewards, not for holding trader collateral or market settlement funds. Efforts to freeze the stolen assets were partially successful, recovering approximately $164,000. Polymarket assured users that its core operations, including market creation and trading, remain unaffected. The incident highlights the importance of regular key rotation and robust security practices in the crypto industry.