Threshold Network announced on X on May 20 that a malicious attacker attempted to mint tBTC on May 18 without depositing underlying Bitcoin (BTC), and the attempt completely failed. Threshold confirmed: no invalid tBTC was generated, and user funds were not threatened. As a precaution, the Optimistic Minting mechanism has been paused.
## Confirmed facts of the incident
According to Threshold Network’s official X post:
Incident time: May 18, 2026, 10:04 UTC (Beijing time 18:04)
Attack method: Attempted to mint tBTC without depositing underlying BTC
Attack result: Failed—no invalid tBTC was generated
User impact: User funds were not threatened
Precautionary measure: Temporarily disabled the Optimistic Minting mechanism
## Optimistic Minting paused: confirmed technical explanation
According to Threshold Network’s official explanation, a comparison of confirmations between the two minting mechanisms:
Base security mechanism (sweeping, currently used):
· Uses a decentralized signer network holding the underlying Bitcoin
· Verifies each native minting using verifiable Bitcoin SPV (Simplified Payment Verification)
· Typical minting time: about 6-7 hours
Optimistic Minting (paused):
Uses a different trust model: deposits are confirmed by the Minter and Guardian (instead of SPV proof)
Typical minting time: about 1.5 hours
Threshold confirmed that pausing Optimistic Minting is a “precautionary measure,” driven by an increase in the frequency of malicious activity across the entire Crypto ecosystem, and not due to a discovery of a vulnerability in the contract itself.
## FAQ
#### Did this attack cause any loss of tBTC funds?
According to Threshold Network’s official confirmation, the attack attempt completely failed—no invalid tBTC was generated, and user funds were not threatened.
#### After pausing Optimistic Minting, is there any impact on existing tBTC holdings or DeFi usage?
According to the official explanation, pausing Optimistic Minting only affects the waiting time for new mints (extended from about 1.5 hours to about 6-7 hours). Existing tBTC holdings and DeFi activity are not affected, and the minting function continues to be provided normally through the sweeping mechanism.
#### What are the main differences between Optimistic Minting and the tBTC base security model?
According to Threshold Network’s official explanation, the base security model uses a decentralized signer network and Bitcoin SPV proofs, with more conservative security assumptions; Optimistic Minting has deposits confirmed by the Minter and Guardian. It mints faster (about 1.5 hours) but uses a different trust model.
