Tether (USDT), a start-up that offers dollar-backed digital tokens, has reported a theft of nearly $31 million from its platform.

The company, which helps exchanges convert fiat currency​ into tokens and aims to serve as a proxy for the U.S. dollar, said in a statement on its website that $30,950,010-worth of its cryptocurrency USDT was taken from its treasury wallet on Nov. 19 and sent to an unauthorized bitcoin address. Tether described the incident as a “malicious action by an external attacker.”

Tether added that the stolen tokens won’t be redeemed but will be flagged to prevent the hacker from exchanging them through its service. The firm plans to release an update of Omni core, its software for partners, in order to lock up the tokens it claims were taken and blacklist the stolen address.

“These builds should prevent any movement of the stolen coins from the attacker’s address,” Tether said in its statement. “We strongly urge all Tether integrators to install this software immediately to prevent the coins from entering the ecosystem.”

Tether also temporarily suspended its back-end wallet service to assist in its investigation. (See also: Gold and Blockchain: An Unlikely Power Couple.)

Bitcoin reportedly dropped as much as 5.4 percent, the most since Nov. 13, on news of the theft, according to Bloomberg. The cryptocurrency has since regained some of those losses.

Tether’s allegations mark the latest in a long line of reported cryptocurrency hacks. Other major victims of thefts from exchanges include Japan-based Mt. Gox and Taiwan-based Bitfinex. Bitfinex, the largest bitcoin exchange platform, lost 119,756 bitcoins, estimated to be worth over $979 million today, over a year ago.

Tether and Bitfinex are believed to have a common owner, according to Coin Desk. This hack has furthered speculation and rumors that the pair have been working together to manipulate the market and that this latest attack on Tether was an inside job. (See also: Bitcoin's Price Crosses $8K for the First Time.)

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