I'm afraid of the coin miners. With virtual digging capabilities - also known as a hashrate - is increasingly concentrated on relatively small holdings, which may increase the risk that diggers will jointly perform attacks to make up 51% of control. Transactional activities or code changes in the blockchain to their will.
There's no need to worry about this because this is very unlikely scenario, if you will look at the Bitcoin hashrate distribution the highest mining pool only got 24% (Btc.com) of share of Bitcoin hash power. Think of this, lets say one of those mining pool obtained 51% shares of Bitcoin hash power and will attempt to attack the network what would they get in return? none right? and why would a mining pool will attempt to attack or destroy the network if this is where they get their money and obtaining 51% will cost you a lot of money to produce more hashrate, they are out of their mind if they will do that, wasting money to destroy your business. 