It's when the miners becomes too centralized basically someone or some group owning more than 50% of the total hashrate that allows them to alter the blockchain data (cmiiw)
from investopedia
The attackers would be able to prevent new transactions from gaining confirmations, allowing them to halt payments between some or all users. They would also be able to reverse transactions that were completed while they were in control of the network, meaning they could double-spend coins.
and as a developer of an ERC20 token there's nothing you can do about it, it's like youre the one who keep inputting the data to the chain (deploying or executing smart contract) and have nothing to do with how the system works except you try to own either nodes or mining rigs to help decentralize the hashrate again.
