A firm specializing in transferring cryptocurrency said Wednesday that hackers have sent back a portion of the digital loot from a record haul.

Poly Network fired off a tweet saying it had received about $4.8 million worth of the stolen assets back, hoping for more from the online heist potentially valued at more than $600 million.

Poly Network had put out a plea for the stolen Ethereum, BinanceChain and OxPolygon tokens to be shunned by traders running "wallets" for storing cryptocurrency.

"The amount of money you hacked is the biggest one in the defi history," Poly Network said Tuesday in a tweeted message to the thieves, using a reference to decentralized finance involving cryptocurrency.

"The money you stole are from tens of thousands of crypto community members."

The return of some of the digital loot came as cyber "white hat" security experts scrutinize the theft and track the thieves.

Blockchain system defense firm SlowMist valued the Poly Network heist at more than $610 million and put out word it is on the hacker's trail.

"The SlowMist security team has grasped the attacker's mailbox, IP, and device fingerprints through on-chain and off-chain tracking, and is tracking possible identity clues related to the Poly Network attacker," the company said in a blog post.

Poly Network threatened police involvement, but also offered the hackers the chance to "work out a solution."

The US Department of Justice and FBI did not respond to requests for comment.

"We are sorry to announce that #PolyNetwork was attacked" and assets transferred to hacker-controlled accounts, the company said in a series of tweets.

Poly Network posted online addresses used by the hackers, and called on "miners of affected blockchain and crypto exchanges to blacklist tokens" coming from them.

Poly Network did not reply to an AFP request for comment, but Twitter users echoed calculations valuing the hackers' haul at some $600 million.

As of the end of April, cryptocurrency thefts, hacks and fraud so far this year totaled $432 million, according to an analysis by CipherTrace.

"While this number may appear to be small when compared to previous years, a deeper look reveals an alarming new trend -- DeFi-related hacks now make up more than 60 percent of the total hack and theft volume," CipherTrace said in a posted report.

That compares to 2019, when defi hacks were virtually non-existent, according to CipherTrace.