BitMEX, a crypto derivatives exchange, pointed out that F2Pool, a bitcoin mining pool, produced an invalid block at height 783426 on April 1, 2023. However, they did not state why and are still investigating the matter.
F2pool produced an invalid bitcoin block
According to BitMEX sponsored node monitoring tool, ForkMonitor, the bitcoin height 783426 produced two blocks. The hash for the invalid block is 00000000000000000002ec935e245f8ae70fc68cc828f05bf4cfa002668599e4.
A bitcoin block is considered valid if it adheres to the protocol rules. BitMEX suspects that the invalid block resulted from bad signature operations. The exchange stated it is still looking into it as they try to explain the anomaly.
BitMEX launched ForkMonitor in 2018 to keep track of hard and soft forks on the Bitcoin blockchain. ForkMonitor is connected to 13 nodes of Bitcoin and its hard forks, including Bitcoin Cash. The tool is also used to detect unintentional consensus bugs.
Invalid bitcoin blocks
Events that could invalidate a mined bitcoin block include double spending, where the same funds are spent twice. The network will confirm one transaction and reject the other as invalid.
Another reason could be when a miner tries to spend bitcoin that they do not own. The network will reject the transaction since the user lacks the necessary funds in their wallet.
A transaction that did not pass script validation and whose time-locked transaction does not meet the lock time is also considered invalid. Bitcoin blocks are released roughly every 10 minutes as set out at the protocol level.
Some miners choose to start mining without validating to get a head start. Still, the risk remains larger than the rewards expected.