Brazil's Mercado Bitcoin halts withdrawals after an attack that Arkham data puts at $46 million, as Tether freezes over 4.5 million USDT

Mercado Bitcoin confirmed on Monday that it had suffered a security incident, days after Binance lost more than $6 billion in what Protos describes as the largest crypto heist on record. "We identified and swiftly contained a security incident in one of our systems early this morning," the São Paulo exchange said in a post on X, according to The Block. It paused deposits and withdrawals as a precaution while it investigates, tracks the assets and works with the authorities.

Arkham data cited by The Block puts the amount taken at about $46.3 million. Emmett Gallic, an analyst at Arkham, said the attacker was sweeping funds out of older deposit addresses and selling memecoins and other altcoins, and, according to Protos, Gallic said the losses were still growing. The exchange said the incident did not affect customers and did not involve a data breach, and it published the wallet addresses that received the funds so blockchain security firms could follow them.

Tether chief executive Paolo Ardoino confirmed that the company froze more than 4.5 million USDT connected to the theft, The Block reported.

The incident follows a string of attacks that The Block lists: Polymarket lost about $2.65 million to a compromised vendor, Chainalysis said its customer data had been accessed, and about a dozen DeFi websites were hijacked and about $138,000 taken.