A 51% attack on the Bitcoin Cash network was successfully executed. The attack was carried out collectively by mining pools BTC.com and BTC.top to reverse a transaction executed by an unknown attacker which took advantage of a bug that allowed the attacker to enter transactions which would normally be deemed invalid. The bug was introduced during the recent hard fork of the Bitcoin Cash network. The 51% attack has raised concerns over the levels of centralization in Bitcoin Cash mining.
Source: CoinDesk