Decentralised financed (DeFi) platform Poly Network says almost all of the US$610 million stolen this month in one of the biggest ever cryptocurrency heists has now been returned by the unknown person or persons behind the attack.
In a Twitter post, Poly Network said it had regained control of all the assets except for US$33 million in a cryptocurrency that had been frozen by the company that manages it.
The network said it was in talks with blockchain platform Tether about unfreezing those funds which Paolo Ardoino, Tether's chief technology officer, froze after the hack.
The hackers had previously said they conducted the attack "for fun" to expose a vulnerability in the platform's digital contracts and it was always their plan to return the tokens.
Some blockchain analysts have speculated they just found it too difficult to launder so much stolen cryptocurrency, particularly with freezes in place.
A lesser-known name in the world of crypto, Poly Network is a platform that facilitates peer-to-peer transactions with a focus on allowing users to transfer or swap tokens across different blockchains.
It announced the hack on August 10, threatening legal action on the hacker. It also wrote an open letter pleading for the funds to be returned.
"Dear Hacker, we are the Poly Network team. We want to establish communication with you and urge you to return the hacked assets," it wrote.
"The amount of money you hacked is the biggest one in the defi history. Law enforcement in any country will regard this as a major economic crime and you will be pursued. It is very unwise for you to do any further transactions.
"You should talk to us to work out a solution," it concluded.
When some of the money started to be returned the network also offered the hacker or hackers a US$500,000 "bug bounty" for finding the issue that allowed the hack in the first place.
But not everyone tried to hold the hacker to account, website Decrypt reported just days after the hack.
An online user tipped off the hacker, telling them to avoid using the blacklisted Tether-based tokens, earning themselves a tip of 13.37 Ethereum cryptocurrency. At the time that was worth around NZ$60,000.
The New Zealand Government recently launched an inquiry into virtual money which will look at the nature, impact and risk of cryptocurrencies.
