Mercado Bitcoin, Brazil's largest cryptocurrency exchange, said Monday that it had suspended deposits and withdrawals after identifying a security incident in one of its systems, as analysts tracked millions of dollars in assets moving off the platform across several blockchains.
What the exchange said
In a statement posted on X, the company said it "identified and swiftly contained a security incident in one of our systems early this morning," adding that there was "no harm to customers" and "no data breach."
Mercado Bitcoin described the suspension of deposits and withdrawals as a precautionary measure, saying its teams were mobilized to investigate, track the assets and coordinate with the competent authorities. The statement followed reports of suspicious transfers from the exchange that appeared to involve the company's own assets rather than customer funds.
The exchange later shared destination wallet addresses that it said held stolen funds.
Estimates of the damage
Security firm Hypernative issued an alert estimating total damages near $40 million worth of cryptocurrency across numerous chains, according to a report from local crypto outlet BitNoticias. The affected chains reportedly included Bitcoin, Ethereum, Solana and Tron.
That estimate reportedly covered about $8.2 million worth of bitcoin, nearly $6.5 million in ether, $1 million in solana and smaller amounts of hundreds of other tokens.
Arkham Intelligence analyst Emmett Gallic said at around 11 a.m. ET that he had tracked more than $46 million in losses so far. "Lots of old deposit addresses are being swept by the hacker currently, while they sell off meme coins and altcoins," Gallic wrote.
Tether CEO Paolo Ardoino said on X that his firm, the largest stablecoin issuer, "froze more than 4.5M USDT related to this security incident."
A run of exchange and platform attacks
The Mercado Bitcoin incident comes days after Binance, the world's largest crypto exchange by trading volume, was hit by a heist that saw $6.3 billion worth of assets pulled from the platform's wallets. Roughly $3 billion of that total was frozen by stablecoin issuers and other centralized exchanges, and the firm said it was using its own funds to replenish the remainder. Customers suffered no losses, according to the company.
That attack replaced last year's $1.5 billion Bybit heist as the largest crypto theft on record. Both the Binance and Bybit attacks have been blamed on North Korean state-sponsored hacking groups, according to statements from U.S. authorities. Binance initially attributed the breach to a compromised engineer's laptop but later said it had discovered "additional points of breach."
Separately, prediction market platform Polymarket disclosed an exploit last Thursday that reportedly swiped $2.7 million from users. Trading was briefly halted while the platform investigated and contained the exploit, which it attributed to a third-party partner, and Polymarket said it would make any affected users whole.
