The funds were stolen in the largest DeFi hack to date on August 10. They were hijacked from Poly Network, which is a cross-chain protocol that lets crypto users swap tokens among blockchains. At this point, the only funds the hacker hasn't returned are the $33m in USDT that were frozen by Tether following the exploit. These can't be moved until Tether authorizes it but the company is working on it.
"We’ll expedite the work with the project to return the funds," Tether CTO Paolo Ardoino told The Block. He added that the company will likely burn the tokens and reissue them in order to pass them to Poly Network, rather than trusting the hacker to move the funds once unfrozen.