Polymarket Users Lose Funds in Hack; Exchange Coordinates with UK Police

Users of Polymarket's international prediction market platform experienced unauthorized withdrawals from their accounts following a security breach linked to a third-party service provider. The incident, which affected an unknown number of traders, prompted Polymarket to suspend trading temporarily and notify law enforcement authorities. The company has also committed to reimbursing any users impacted by the theft.

The breach did not affect Polymarket's U.S. exchange, which remains secure. Initial reports from traders surfaced on social media on Thursday afternoon, with many noting unexpected fund withdrawals. In response, Polymarket halted operations on its international platform to investigate the issue and resolved the vulnerability by 3 p.m. Eastern Time, at which point trading resumed.

Later communications in a Discord chat room clarified the reimbursement process for affected users. Those who lost less than $10,000 will have their funds restored by October 30. Users with losses exceeding that amount will be required to sign a release form before receiving compensation. This distinction aims to streamline the refund process while addressing larger claims with additional verification.

According to a source familiar with the situation, the root cause of the breach traces back to DebugBear, a website performance monitoring company based in the United Kingdom. DebugBear confirmed via an X post (formerly Twitter) that it suffered a security incident on the same day. Given DebugBear's UK location, Polymarket has involved British law enforcement to assist with the investigation. Attempts to obtain a direct comment from DebugBear were unsuccessful at the time of reporting.

Two analytics firms specializing in blockchain and prediction market activity, Betting Intelligence and Polysights, analyzed publicly available on-chain data related to the incident. Their findings reveal that a single Polymarket account executed withdrawals totaling at least $2.7 million, dispersing funds into 710 separate wallets. Dan Zimmermann, Chief Intelligence Officer at Betting Intelligence, described the event as a "significant and new form of breach" for Polymarket. He noted the timing, just before the U.S. midterm elections, as particularly concerning, emphasizing the need for heightened security awareness in the sector.

Polymarket's international platform functions as a decentralized finance (DeFi) marketplace on the Polygon blockchain network. Unlike its U.S. counterpart, the international exchange operates outside U.S. regulatory oversight. This decentralized structure can offer benefits but also presents unique challenges in security and compliance.

The timing of the hack is notable as both Polymarket’s U.S. and international exchanges anticipate increased user activity ahead of the midterm elections scheduled for November 3, 2026. Prediction markets often see surges in volume during major political events, making security incidents especially disruptive and impactful.

This is not the first time Polymarket has faced such challenges. In June, the company reported a similar security issue involving a third-party vendor compromise. At that time, Polymarket also promised to refund affected customers, demonstrating a pattern of reliance on external service providers that introduces potential vulnerabilities.

The broader prediction market industry, which allows users to speculate on outcomes of future events including elections, sports, and economic indicators, continues to grow globally. Platforms like Polymarket leverage blockchain technology to offer decentralized trading options, but the sector’s rapid expansion highlights ongoing concerns about cybersecurity and regulatory frameworks.

As digital assets and decentralized finance platforms become more mainstream, incidents like this underscore the importance of rigorous security practices and responsive risk management. For traders and investors, understanding the risks involved with third-party integrations and decentralized exchanges remains critical.

Polymarket's swift action to halt trading, coordinate with authorities, and commit to reimbursements reflects efforts to maintain user trust amid setbacks. The investigation by UK law enforcement and the response from involved parties will be closely watched by industry participants and regulators alike in the coming weeks.