Symbiosis shut its native Bitcoin bridge on September 11, 2026, after an attacker exploited the BridgeV2 contract to mint unbacked synthetic Bitcoin tokens on BNB Chain and Ethereum. Reports differ sharply on the volume created, ranging from about 46 billion to 369 billion syBTC in the latest account versus more than 2^62 syBTC in the earlier incident classification. The attacker converted only about 4.39 WBTC on Ethereum, extracting roughly $336,000 in real value. Symbiosis said it detected evidence of the attack at about 04:28 UTC and immediately halted BTC routing, while other routing protocols continued operating. The incident, classified as DCI-2026-304 in the Delta Incident Archive, was attributed to BridgeV2 processing an incorrect message. The exploit did not compromise Bitcoin itself but exposed weaknesses in infrastructure used to move BTC into DeFi. BridgeV2 connects Symbiosis's Portal and Synthesis contracts with an off-chain Relayers Network, whose transactions use a Multi-Party Computation (MPC) key stored in the contract. MPC threshold signatures help secure native BTC in a Portal while allowing relayers to create syBTC on another blockchain, where it can be converted into a user's preferred asset. Symbiosis said Decurity audited the native BTC bridge. DeFiLlama classified the incident as an Unbacked Cross-Chain Mint. The episode followed a $320 million Liquid Network breach and added to concerns over recurring cross-chain failures. TRM Labs recorded 207 crypto hacks in the first half of 2026, the highest semiannual total in its history, although aggregate losses fell to $972 million from $2.3 billion in the first half of 2025. DeFiLlama estimates total bridge losses of at least $3.68 billion. The Bank Policy Institute's analysis of the KelpDAO hack found that unbacked rsETH created through weak cross-chain validation contributed to stress on Aave, followed by $5 billion in stablecoin withdrawals and a borrowing interest rate that rose to 10%.