Ethereum has "difficulty bombs" about once a year which effectively force the network to follow along with protocol changes made by the Ethereum Foundation. The

Ethereum has "difficulty bombs" about once a year which effectively force the network to follow along with protocol changes made by the Ethereum Foundation. They could conceivably use that same mechanism to exponentially slow the network below the point of usability by waiting for the hardcoded block and then... doing nothing. Afaik bitcoin doesn't have anything like that.