For those who do not know about 51% attack:
The attack on Bitcoin Gold was first discovered on May 18. After the hacker gained control of the network, they engaged in double spending, in which they sent Bitcoin Gold to various cryptocurrency exchanges and also sent the same BTG to their own wallet. It was discovered that 388,200 BTG was sent to one address since May 16.
If all of that BTG is associated with the double spending, then the attacker stole around $18.6 million USD. During the attack, the hacker was able to reverse transactions as far back as 22 blocks, which has led to some calls for increasing the confirmation requirements to 50 blocks.
Verge (XVG) Cryptocurrency Got Hacked, 51% Attack
Bitcoin gold is a project led by Jack Liao of Hong Kong mining firm Lightning ASIC seeking to change the proof-of-work (PoW) algorithm and promising to enable common people to mine using ubiquitous, low-cost graphics cards. It’s worth noting, however, that this accessibility means attacking the system will also be cheap, which Dr. Craig Wright, chief scientist of the nChain Group, has previously pointed out.