The suspected hacker behind one of the biggest cryptocurrency heists has revealed that he did it “for fun.” More than $600 million in cryptocurrency assets was stolen Poly Network, a decentralised finance (DeFi) platform.

DeFi platforms function as financial platforms without traditional middlemen like banks and institutions being involved, theoretically making lending and borrowing easier for everyone involved.

Poly Network revealed the hack on August 10, and tweeted to hackers asking them to return the stolen assets. Since then a series of bizarre incidents has followed.

“We want to establish communications with you and urge you to return the assets,” the company tweeted.

“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. The money you stole (sic) are from tens of thousands of crypto community members, hence the people,” added the company.

Surprisingly enough, the hacker heeded the call. The hacker returned $342 million worth of crypto to the platform by August 12, according to Poly Network.

But the hacker did not just return the money, a unique Q&A session followed. The hacker embedded messages within the transactions themselves, giving some insight into the change of heart.

“That’s always the plan! I am _not_ very interested in money! I know it hurts when people are attacked, but shouldn’t they learn something from those hacks?” the hacker said.

The suspected person said he hacked the platform “for fun” after becoming aware of the potential “bug” on Poly Network’s systems.

“When spotting the bug, I had a mixed feeling,” the person said.

“Ask yourself what to do had you facing so much fortune. Asking the project team politely so that they can fix it? Anyone could be the traitor given one billion!”

“I can trust nobody!” the person continued. “The only solution I can come up with is saving it in a _trusted_ account while keeping myself _anonymous_ and _safe_.”

Experts suggest the money was returned due to the fact that laundering cryptocurrency on any open blockchain ledger was harder than simply stealing it.

It is yet to be seen whether the hacker will return all of the money.

Tom Robinson, chief scientist at blockchain analytics firm Elliptic, said the person writing the Q&A was “definitely” the hacker behind the Poly Network attack.

“The messages are embedded in transactions sent from the hacker’s account,” Robinson told CNBC. “Only the holder of the stolen assets could have sent them.”

CNBC could not independently verify the authenticity of the message, and the hacker, or hackers, have not been identified.

(Edited by : Shoma Bhattacharjee)