Part 6/12:
Old Bitcoin addresses (P2PKH), which rely on a public key remaining undisclosed until a transaction, are particularly vulnerable. When a coin transaction occurs, the public key becomes exposed, potentially providing a quantum adversary with the information needed to crack the code. By transferring their holdings to modern SegWit and Taproot addresses, which conceal public keys until they are explicitly revealed during spending, the wallet owner has effectively "retired" the vulnerable addresses.
This move can be seen as a form of cryptographic insurance—a long-term health check for one of the earliest and most valuable Bitcoin holdings. It's a sign of immense foresight, indicating the owner’s desire to preserve their wealth against a future quantum breakout.