Threshold Network said an attacker attempted to mint tBTC without depositing the required underlying BTC on May 18 at 18:04 Beijing time. The protocol stated that no invalid tBTC was created and user funds were not at risk. In response, Threshold Network paused Optimistic Minting and moved minting to the sweeping mechanism, increasing processing time from about 1.5 hours to roughly 6 to 7 hours.