If they pushed for people upgrading to 0.8 then everyone not upgrading would have their own blockchain. By getting more than 50% of the users to use 0.7, the re

If they pushed for people upgrading to 0.8 then everyone not upgrading would have their own blockchain. By getting more than 50% of the users to use 0.7, the rest of the 0.8 clients will discover that everyone else uses the 0.7 chain and thus replay all of the transactions on that chain. Upgrading: Those who doesn't upgrade end up with their own chain. Downgrading: Those who doesn't downgrade will automatically use the other chain when it becomes dominant. > But with two separate blockchains, wouldn't both be vulnerable? It's only the chain that doesn't become the main chain that is vulnerable. Because they're pushing for 0.7 to be the main chain you don't have to worry about double spending there.