Sad to see another PoW coin come under 51% attack. The long term solution to attacks like this is to migrate to Avalanche. https://twitter.com/firoorg/status/1351703001849757697

Remember that PoW's safety depends solely on the amount of hardware that is available to launch a 51% attack. If an attacker has 51% hashpower, the number of confirmations required for safety is infinity -- the coin is not safe to use.

Changing the hash function is something that people try, but it typically doesn't work: once the coin is turned into a GPU-mined coin, the attacker has as much hardware to attack with as there are GPUs to rent.

Another temporary fix is to add "checkpoints" or "chain locks," where some blocks are encased in stone when they are k blocks deep. These mechanisms are not safe or sound. Let me explain.

Imagine an attacker with 51% power. Imagine chain locks that make a block X1 permanent when it's k deep. A smart attacker can release a chain of length (k+1) starting with block X2, just as some portion of the network is making permanent X1. Now you have a fork.

That fork is permanent and can contain a double spend. Sure, this requires getting the timing right, but the attacker has all the time in the world. And sure, it could be costly if k is high, but it will eventually succeed.

There's another strategy, which is to use "master nodes" to make a certain block in the chain permanent and prevent reorgs.

This approach renders PoW completely pointless. Nothing is permanent unless decided by the master nodes.

An exchange should never accept payments unless the payment is buried under a block that has been decided by the master nodes. PoW accomplishes nothing when it comes to decision making or security. The coin is effectively centralized, managed by the master nodes.

51% attacks are nature's way of garbage collecting insecure chains. Ultimately, they turn into centrally managed chains.

The only actual solution is to switch to a protocol that isn't vulnerable to 51% attacks.

Objectively speaking, Avalanche is the state of the art consensus protocol. It offers maximal decentralization, low latency, and high throughput. Switching to it is the sensible thing to do.