• Official statement (12:56 UTC, Nov 2): Mercado Bitcoin says it "identified and quickly contained" a security incident in one of its systems overnight, with no losses to customers and no data leak. Deposits and withdrawals are suspended as a precaution while teams investigate, trace the assets and coordinate with authorities. It has not given a loss figure.
• Update (14:24 UTC): the exchange published destination addresses tied to the incident for tracking: EVM 0xe485e7A70b1131216Cb47CA4555c4Bbb2C742478, BTC 19qGpsHvzh1t6pVi526XNNkh6hW6prDZp, SOL 3YX6WHncP1Ra4AotE9YLawFt4nPmxyux288FWXkEW97J, Tron TEX3HuDRHRa3tnYpy96M4UfSx62VhDyA5L, plus a Stellar address.
• On-chain check: the BTC address has received 106.07 BTC in 7 transactions and had spent none when this item was written (Blockstream explorer).
• Third-party estimate (not confirmed by the exchange): Hypernative, as reported by Unchained, says the outflows were plain transfers rather than a smart-contract exploit, that most funds moved between 06:19 and 06:53 UTC with Bitcoin deposit-address sweeps starting at 02:15 UTC, and that the attacker holds about 2,852 ETH, 106 BTC, 10,700 SOL and 6.7M XLM plus 200+ other tokens, more than $40 million in total.
• Freeze: Tether CEO Paolo Ardoino says Tether froze more than 4.5 million USDT related to the incident.

Not known: how signing access was obtained, and whether this is linked to any other recent exchange theft; neither the exchange nor Hypernative has tied it to the Oct 29 Binance theft. For other custodians: plain transfers from hot and deposit wallets point to key or signing-service compromise rather than a contract bug, so alert on deposit-address sweeps to new destinations outside normal consolidation windows and cap automated signing per time window.