Brazil’s Largest C...

Brazil’s Largest Crypto Exchange Hit by Security Breach Days After Binance Hack

By José Oramas November 03, 2026 In Brazil, Crypto Exchange, Security

Mercado Bitcoin halted deposits and withdrawals on Monday after a breach that Arkham estimates cost at least US$46 million (AU$65.8 million).
Tether CEO Paolo Ardoino said the stablecoin issuer froze more than 4.5 million USDT tied to the incident.
The exchange told customers they will lose no assets, while Bitquery reported deposit addresses still being emptied hours after MB said it had contained the attack.

Mercado Bitcoin (MB), Brazil’s largest crypto exchange, has suspended access to its services after an attacker drained its wallets on Monday, days after North Korean hackers’ record theft from Binance.

Blockchain analytics firm Arkham estimates the attacker took at least US$46 million (AU$65.8 million) across multiple blockchains. Its trace shows the attacker draining 2,852 ETH, worth US$6.52 million (AU$9.32 million), at 6:24 a.m. UTC. None of MB’s posts on X has put a figure on the attacker’s haul.

MB first reported the breach on X at 12:56 p.m. UTC, saying it had contained an attack on one of its systems overnight. It paused deposits and withdrawals as a precaution and said no customer data had leaked. The attack hit the exchange’s hot wallets, and the cold wallets that hold most client assets were untouched, MB told Brazilian news agency Estadão Broadcast.

“Mercado Bitcoin assures you that you will not lose any assets as a result of the security incident we identified today on our platform,” the exchange wrote in Portuguese at 11:17 p.m. UTC.

MB also told Bloomberg it would absorb the loss itself. It said it is working with the authorities but has not named them.

Tether Freezes Linked USDT

Tether CEO Paolo Ardoino posted at 3:06 p.m. UTC that the stablecoin issuer had frozen more than 4.5 million USDT connected to the incident. On-chain data firm Bitquery later counted US$7.3 million (AU$10.44 million) frozen by Tether and stablecoin issuer Paxos combined.

Tether is also an investor in the exchange. It announced a US$20 million (AU$28.6 million) investment in MB on 7 July, as part of a funding round that included SoftBank. Tether’s release described MB, founded in 2013, as serving 4.5 million users.

Deposit Addresses Kept Draining

Bitquery puts the total taken at US$48.5 million (AU$69.4 million). Its analysis found the exchange’s hot wallets on 10 chains paid the attacker within about 25 minutes.

Bitquery also reported that 35,853 customer deposit addresses on Ethereum sent their balances to the attacker from 12:10 p.m. UTC. Those transfers, worth about US$261,000 (AU$373,000), ran until at least 3:44 p.m. UTC. By Bitquery’s account, that was more than two hours after MB said it had contained the attack.

MB applied to Brazil’s central bank for authorisation on 27 October, days before the breach, according to Estadão Broadcast. Under the Banco Central do Brasil’s licensing rules for crypto service providers, firms already operating had until 30 October to apply. The rules, in force since February, hold licensed firms to banking-style standards on governance, consumer protection and cybersecurity.