GMX offered a 10% "bug bounty" to the hacker if they returned the funds. The attacker later returned $40.5 million in stolen assets; unusually, this is more than the 90% return requested by GMX.
GMX exchange hacked for $42 million
The decentralized perpetual exchange GMX has been exploited for $42 million. The exploit involved a vulnerability in one version of the exchange's price calculation smart contract. GMX paused some trading while they investigated the hack, and placed other temporary restrictions on the platform.