Poly Network was created by a collaboration between multiple blockchain providers, namely, Neo, Ontology and Switcheo to enable users to exchange tokens across different crypto platforms, including Bitcoin and ETH. Poly Network CEO, Changpeng Zhao, tweeted that the value of stolen assets to be at least $611 million, making this the largest DeFi hack thus far. The attacker wallet addresses associated with this incident are: 0xC8a65Fadf0e0dDAf421F28FEFEAb69Bf6E2E589963. Tether has since blacklisted the USDT on ETH worth $33 million of tokens, that was stolen in this attack.
Source: https://www.bleepingcomputer.com/news/security/over-600-million-reportedly-stolen-in-cryptocurrency-hack/