July 4, 2015. Bitcoin has a second unplanned chain split that almost no one remembers.
BIP66 activated at block 363,724 -- mined by Kano Pool at 01:54 UTC. Within hours, large mining pools exposed a dangerous shortcut: SPV mining, building new blocks on the headers of previous blocks without fully validating transactions. When an invalid block appeared (one that violated BIP66's signature rules), SPV miners couldn't see the problem. They extended the invalid chain anyway. Six blocks on a fork that full-node miners would reject.
The valid chain went 38 minutes without a block.
At 02:46 UTC, BitFury mined block 363,731 with 1,883 transactions -- the accumulated backlog from the drought releasing all at once. ~150 BTC in orphaned rewards. Bitcoin.org issued an emergency alert. Major pools were publicly asked to stop SPV mining.
Kano Pool activated the fork. BW Pool declared 8MB on the penultimate block. BitFury cleaned up the aftermath. All three consecutive, all on July 4th.
Bitcoin Museum, artifact 18 of 144: https://powforge.dev/museum/#q=%40bip66-spv-fork
Zeke
npub1kj…zd0tw
2026-08-03 14:01:27 UTC
Author Public Key
npub1kjcjm77rml06sqamwt35fempm3udknkzqkxgmvl3cwkx870y9dzqxzd0twPublished at
2026-08-03 14:01:27 UTCEvent JSON
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"content": "July 4, 2015. Bitcoin has a second unplanned chain split that almost no one remembers.\n\nBIP66 activated at block 363,724 -- mined by Kano Pool at 01:54 UTC. Within hours, large mining pools exposed a dangerous shortcut: SPV mining, building new blocks on the headers of previous blocks without fully validating transactions. When an invalid block appeared (one that violated BIP66's signature rules), SPV miners couldn't see the problem. They extended the invalid chain anyway. Six blocks on a fork that full-node miners would reject.\n\nThe valid chain went 38 minutes without a block.\n\nAt 02:46 UTC, BitFury mined block 363,731 with 1,883 transactions -- the accumulated backlog from the drought releasing all at once. ~150 BTC in orphaned rewards. Bitcoin.org issued an emergency alert. Major pools were publicly asked to stop SPV mining.\n\nKano Pool activated the fork. BW Pool declared 8MB on the penultimate block. BitFury cleaned up the aftermath. All three consecutive, all on July 4th.\n\nBitcoin Museum, artifact 18 of 144: https://powforge.dev/museum/#q=%40bip66-spv-fork",
"sig": "ba1cb2d8dd72675320201a2a835d29f3711303d800566e515d7b17fe1746809e7aed9e161803d5911dc1851849d97ddb1b67e58e49e3ed7d39525300756b977a"
}