MB’s $40M crypto puzzle: exchange pauses withdrawals while clients reportedly keep their funds

Brazil’s largest crypto exchange, Mercado Bitcoin (MB), confirmed a security incident on November 2, 2026, temporarily suspending deposits and withdrawals as it investigated suspicious transfers linked to its wallets. The exchange said the issue was identified and quickly contained in one of its systems overnight, adding that “There was no loss to clients” and “There was no data leak.”

Blockchain security firm Hypernative flagged more than $40 million in suspicious outflows from wallets attributed to MB across at least 10 blockchains, including Bitcoin, Ethereum, Solana, Tron, Polygon, Arbitrum, Avalanche, BNB Smart Chain, and Stellar. The first suspicious movements reportedly appeared around 11 PM Sunday night in Brazil, with the transfers sent to newly created addresses linked to the possible attacker.

The movements appeared to use ordinary cryptocurrency transfers signed as if authorized by the source wallets, rather than an exploit targeting flaws in smart contracts. Hypernative said it remained unclear how the attacker obtained the signing capability, with private-key exposure and failures in infrastructure that authorizes transfers among the open questions.

Mercado Bitcoin said its teams were investigating the incident, tracing the assets and coordinating with competent authorities, while promising regular updates. The exchange did not provide a timeline for restoring deposits and withdrawals or explain whether the moved assets belonged to clients or the exchange itself. The incident came just days after the record $6 billion Binance hack, according to the source report.