The Spam War Vs The Blocksize War History rhymes again A section of the anti-spam camp are now considering tinkering with Bitcoin's fork choice rule. This is what Bitcoin Unlimited did in 2017, in the Blocksize War, with the "acceptance depth" and "excessive block" parameters. This system was fundamentally flawed and merchants running this would be exposed to double spend attacks In the below post, it is suggested to "simply wait 1 minute before accepting a [spam block] as valid". Like Bitcoin Unlimited, this is a departure from a key principal in Bitcoin, that a block is either valid or invalid. A merchant adopting this 1 minute rule, could be leaving themselves open to double spend attacks For instance, an attacker could keep making large Bitcoin transactions to themselves and hope the transaction is included in a "spam block". Then, as soon as the spam block confirms, broadcast a conflicting transaction, which is a deposit to an exchange or merchant, which you hope gets mined in a non spam block within a minute. Or you could mine this yourself to attack a victim merchant. Even if the spam chain has more blocks, the merchant, if following the one minute rule, could credit the deposit in the conflicting non-spam chain. Then after the minute expires, the deposit vanishes from the merchants wallet.(BitMEX Research)