Original author: Sanqing, Foresight News

According to French media Le Monde, on April 6 and 15, the weather sensors at Paris Charles de Gaulle Airport experienced two anomalies, with temperatures rising over 3°C in just a few minutes, only to drop back down as if nothing had happened. Behind each anomaly, someone had predicted the corresponding low-probability temperature range on Polymarket in advance, collectively earning about $34,000 from a principal of several dozen dollars. The account that placed the first bet was created just two days before the anomaly occurred.

Météo-France subsequently conducted a physical examination of the sensors and found signs of human interference, filing a criminal complaint with the gendarmerie at Charles de Gaulle Airport for "interfering with an automated data processing system." According to an analysis from an AR15 forum post, under Article 323-2 of the French Penal Code, and since Météo-France is a public institution, the related charges could potentially carry sentences of up to 7 years in prison and fines of €300,000.

The technical level of this scam is nearly zero

The settlement chain for Polymarket's Paris temperature market is as follows: physical sensor → Météo-France → Weather Underground → Polymarket contract.

On this chain, the smart contract part is audited, the data transmission is automated, and the data scraping from Weather Underground is also real-time. The only vulnerability is at the very beginning: a thermometer standing by the airport roadside, with no fencing, no cameras, where anyone can walk past.

The only tool the attackers needed was a hairdryer that could take batteries.

Polymarket relies on the highest temperature of the day, which means a brief spike in temperature is all that is needed to overwrite the official record for the day.

It was more ideal to act in the evening or at night, as the highest daytime temperature usually had passed, making later readings more likely to become new records. Thus, the suspects chose to act at 7 PM on April 6 and at 9:30 PM on April 15.

The operation process roughly involved: purchasing low-probability options in advance, walking to the sensor at night, turning on the hairdryer, waiting for the reading to cross the target temperature, then leaving and waiting for the on-chain settlement.

The entire operation had no technical complexity, only requiring some understanding of the settlement mechanism and a pair of legs willing to walk to the airport's edge.

Polymarket's response: quietly replaced the thermometer

Polymarket has not issued any official statement regarding this matter. The only thing it did was change the data source for the Paris temperature market's settlement from Charles de Gaulle Airport (LFPG) to Orly Airport (LFPB).

The profits from the two accounts were not revoked, and the market settled normally according to the on-chain records.

The sensors at Orly Airport are similarly exposed outdoors and also lack physical protection. The address was changed, but the problem remained the same.

This is not the first controversy for Polymarket. In October 2024, a French trader was accused of manipulating Trump election odds using four affiliated accounts, reportedly profiting $85 million; in March 2025, a whale used 5 million tokens to force UMA governance voting, settling a controversial market with a "yes," involving $7 million; in January and March 2026, there were unusual bets related to Venezuela and Iran markets, the latter of which has drawn attention from the U.S. Congress...

Previous instances required at least a few million dollars in chips or governance tokens; this time, the cost was just a hairdryer.

The contract was audited, but the thermometer was not

This story has a sense of absurd humor. A prediction market operating on blockchain, marketed for its decentralization and immutability, was rubbed to the ground twice by a battery-operated hairdryer. Cryptography could not help in this matter, as it never verifies whether the input data is real.

Polymarket currently has 173 active weather markets, and the settlement basis for these markets is mostly based on a certain physical sensor from somewhere.

A sensor, when used as a meteorological tool, gains credibility from the absence of anyone motivated to tamper with it. Polymarket introduced a new incentive structure but provided no new physical protection.

The thermometer from Météo-France diligently recorded the temperatures it sensed. It just did not know that it had become a financial settlement terminal.

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