Investigators have uncovered a sophisticated Polymarket betting fraud scheme where fraudsters manipulated thermometers in Paris to rig payouts on the popular online betting platform. France’s national weather service, Météo-France, reported the suspected tampering to police after recording a series of abnormal temperature spikes that coincided with large wins on Polymarket, according to BFMTV.
Meteorologists filed a police report over suspicions of physical interference with official temperature sensors.
Chronology of Polymarket betting fraud spikes
The first incident occurred on April 6, 2026, at the Charles de Gaulle Airport weather station. This station serves as the reference point for determining maximum temperatures in Paris.
Between the morning and 6:00 p.m., the temperature did not exceed +18°C. The platform estimated a 95% probability that this would remain the daily high. However, the sensor suddenly recorded a jump of more than 3 degrees in the evening, reaching +21°C before quickly returning to normal. At that exact moment, a Polymarket user whose account was registered just two days prior won $14,000 on a bet of only a few dozen dollars.
A second similar case occurred on April 15. While temperatures remained stable around +18°C to +19°C, the sensor abruptly showed +22°C in the evening. In just half an hour, the probability of such an outcome on the platform surged from 0.1% to 95%. An unknown user earned more than $20,000 from the bet.
Fraud mechanism: physical intervention
Specialists believe such temperature fluctuations over such short periods cannot be caused by natural weather conditions.
French meteorologist Ruben Hallali explained that the scheme would require physical access to the equipment. Someone familiar with the weather station’s design could approach the sensor and use a portable heating device to briefly raise the temperature by the necessary 2–3 degrees to ensure a winning bet.
Polymarket reaction
Public disclosure of the incidents forced the betting organizers to take urgent measures to prevent further manipulation. Polymarket officially changed the data source for Paris weather. The platform now uses readings from the Le Bourget Airport weather station as the reference sensor for bets on the French capital’s maximum temperature.
