A cryptocurrency exchange that claims real dollars back its popular digital coin Tether raided those reserves to cover up $850 million that went missing, the New York Attorney General’s office said Thursday.

State Attorney General Letitia James said Hong Kong-based iFinex Inc., which operates the Bitfinex cryptocurrency exchange and owns Tether Ltd., has been commingling client and corporate funds to cover up the missing funds, which occurred in mid-2018 and hadn’t been disclosed publicly.

The attorney general’s office said it has obtained a court order directing iFinex to stop moving money from Tether’s reserves to Bitfinex’s bank accounts, halt any dividends or other distributions to executives and turn over documents and information. The coverup drained at least $700 million from Tether’s reserves, according to the attorney general’s office.

Bitfinex released a statement on its website, arguing the attorney general’s filings were “written in bad faith and riddled with false assertions” and characterized them as an overreach. The company said it had previously been cooperating with the attorney general office’s investigation, and it planned to fight the order.

The attorney general’s findings emerged from an investigation into cryptocurrency exchanges that it launched in 2018 and is continuing. A report in September warned that many exchanges lacked basic safeguards and left consumers vulnerable to exploitation by market manipulators.