BIP-30 by Pieter Wuille.

This and let’s not forget the inflation bug fix that in reality confiscated *billions* of Bitcoins. nostr:nevent1qqs2crcktegr40k5nf0j30dp4v3dqxff9cm6due230qt42t3kjm8gtspz3mhxue69uhkummnw3ezummcw3ezuer9wc2gukfp