Fraudsters made an attempt to steal at least $10 million through Polymarket using stolen debit cards. They funded accounts, placed trades, and then sought to withdraw the money to different cards or accounts they controlled, as reported by The Wall Street Journal.
According to their findings, the attack began in February, with approximately seven accounts being the main focus. One account alone made around 4,000 deposit attempts.
Checkout.com, the payment processor, flagged over 80% of the deposits for Polymarket US as fraudulent at one point, while the industry average hovers around 1%.
Since most of the suspicious deposits were blocked, the exact loss amount remains unclear.
Polymarket's Response to the Attack
As suspicious activity surged, regular customers faced delays in withdrawals. To expedite the processing of requests, Polymarket allowed funds to be transferred not only to the original payment source.
This restriction typically complicates the withdrawal of funds obtained via stolen cards. According to the WSJ, some staff warned that lifting this restriction could increase the risks of fraud and money laundering.
Management believed that other control mechanisms were adequate.
Subsequently, the platform limited the number of debit cards that could be linked to a single account. By May, the proportion of fraudulent transactions returned to industry-average levels.
A Polymarket representative stated that the company is cooperating with regulators and law enforcement. An audit by the law firm Sullivan & Cromwell confirmed that the platform adhered to regulatory requirements.
In late July, the platform faced another scheme: criminals used stolen personal information to access accounts of nearly 500 clients without knowing the usernames and passwords. Polymarket promised to compensate the losses.
Kalshi Accused of Inflating Trading Volumes
A trader under the alias Beni accused Kalshi of artificially inflating its cryptocurrency trading volumes. He cited a perpetual futures contract on Ethereum as evidence: with an open interest of about $3.1 million, its daily turnover was approximately $538.6 million.
This thread is 100% gonna blow up and I am gonna look like a salty c****again but @icobeast pissed me off so now it's gonna get ugly
Kalshi fakes their crypto volume and I can prove it
NOTHING pisses me off more than watching a company treat its own customers like complete… https://t.co/1LWMVGVaeU
— Beni (@beniduboss) September 19, 2026
Beni also referenced Kalshi's incentive program for perpetual contracts. According to the terms registered with the CFTC, the taker fee for cryptocurrency instruments after a rebate is 0.3 basis points, while the maker receives a payment of 0.3 points.
The trader suggested that the low aggregate transaction value could encourage artificial trading volume.
However, the program’s rules explicitly exclude self-trading, wash trades, and pre-arranged transactions from rewards. Kalshi reserves the right to deny payments and initiate investigations if violations are suspected.
The head of the platform's cryptocurrency division, using the alias IcoBeast, dismissed the accusations. He stated that the initial criticism conflates two different products: data from Artemis pertained to prediction markets, while the rewards program applies to perpetual futures.
There is no such rewards program for cryptocurrency contracts based on event outcomes.
Hey Beni,
Seems like a bunch of wires got crossed here so I just wanted to set the record straight. Your original claim was that Kalshi’s crypto prediction market volume was fake. The chart from Artemis shows prediction market volume share, not perps. We don’t do rebates for… https://t.co/RudV9qzDNn pic.twitter.com/QSIpBu0Cm5
— IcoBeast.eth🦇🔊 (@icobeast) September 20, 2026
As of September 21, there have been no public decisions from the CFTC, audits, or data regarding specific accounts that would confirm allegations of fictitious trading on Kalshi.
The figures presented by Beni are based on his own estimates and do not, on their own, prove the occurrence of such trades.
It is worth noting that in June, WSJ journalists conducted an investigation revealing that Polymarket paid content creators for videos featuring fake bets and winnings on imitation sites.