While there is still no clear idea of who is responsible for the manipulation of ETC’s blockchain by controlling the majority of CPU power in the mining pool, the circumstances raise some big questions concerning the security and power of proof-of-work (PoW) algorithms.
It is worth taking a look at the chain of events leading up to the confirmation that ETC had indeed been the target of a blockchain reorganization.
On Jan. 7, ETC developers were alerted of a possible attack on the network by Chinese blockchain security firm SlowMist, which was relayed to the wider community on Twitter.
CCN | https://cointelegraph.com/news/ethereum-classic-51-attack-the-reality-of-proof-of-work
The only best answer to creating more protection to the POW by applying ASIC resistant to block it.
BTG has applied it and it has not been getting 51% attack again. For me I will prefer to use hybrid system rather than put them all into the POW system.