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A lesser-known name in the world of crypto, Poly Network is a decentralized finance (DeFi) platform that facilitates peer-to-peer transactions with a focus on allowing users to transfer or swap tokens across different blockchains.

For example, a customer could use Poly Network to transfer tokens such as bitcoin from the Ethereum blockchain to the Binance Smart Chain, perhaps looking to access a specific application.

According to specialist crypto website Coindesk, Poly Network was launched by the founders of Chinese blockchain project Neo.

Poly Network operates on the Binance Smart Chain, Ethereum and Polygon blockchains. Tokens are swapped between the blockchains using a smart contract which contains instructions on when to release the assets to the counterparties. One of the smart contracts that Poly Network uses to transfer tokens between blockchains maintains large amounts of liquidity to allow users to efficiently swap tokens. Poly Network tweeted on Tuesday that a preliminary investigation found the hackers exploited a vulnerability in this smart contract.

According to an analysis of the transactions tweeted by Kelvin Fichter, an Ethereum programmer, the hackers appeared to override the contract instructions for each of the three blockchains and diverted the funds to three wallet addresses. These were later traced and published by Poly Network.

The attackers stole funds in more than 12 different cryptocurrencies, including ether and a type of bitcoin, according to blockchain forensics company Chainalysis. A person claiming to have perpetrated the hack said they had spotted a "bug," without specifying, and that they wanted to "expose the vulnerability" before others could exploit it.

As of late Wednesday, the hackers had returned $260 million of the assets, but $353 million was outstanding. It is unclear where the remaining assets have gone.

Coindesk reported on Tuesday that the hackers had tried to transfer assets including tether tokens from one of the three wallets into liquidity pool Curve.fi, but that transfer was rejected. About $100 million has been moved out of another of the wallets and deposited into liquidity pool Ellipsis Finance.

The hacker or hackers has not yet been identified. Cryptocurrency security firm SlowMist said on its website that it has identified the attacker's mailbox, internet protocol address, and device fingerprints, but the company has not yet named any individuals. SlowMist said the heist was "likely to be a long-planned, organized and prepared attack."

Despite the purported hacker posing as a so-called "white hat", an ethical hacker who aimed to identify the vulnerability for Poly Network and had "always" planned to give the money back, according to the messages published by Chainalysis, some crypto experts are skeptical.