A few updates this week in the world of mining:
Bitcoin SV (BSV) conducted a hardfork which resulted in a non-trivial number of nodes remaining on an incompatible version. This caused a brief chain split that appears to have been resolved as of this writing.
Researcher Hasu describes a new form of 51% attack called the “Purge” attack in which an attacker with sufficient hashing power replaces a number of the most recent blocks with empty blocks, sending previously confirmed transactions back into the mempool.
This could create a scenario in which ill-prepared merchants and transaction recipients, who may have considered payments sufficiently finalized, have to deal with potential double-spends as these transactions are effectively reverted to zero-conf status.
As with all of these novel attack scenarios, they are still theoretical, but it is interesting and important to understand these potential attack vectors.