NEW YORK, Aug 12 (Reuters) - Hackers behind one of the biggest ever digital coin heists have now returned nearly all of the $610 million-plus they took, the cryptocurrency platform targeted by the hack said on Thursday. Poly Network, a platform that facilitates peer-to-peer transactions, said on Twitter here that the tokens were transferred to a multi-signature wallet controlled by the company and that it was carried out by what it now characterizes as an ethical "white hat" hacker. (Reporting by Gertrude Chavez-Dreyfuss; Editing by Chizu Nomiyama