Cryptocurrencies fell amid reignited regulatory worries and questions around the legitimacy of so-called "stablecoin" tether.

The entire market shed about $10 billion in value in the space of an hour late Thursday, CoinMarketCap data showed. This after the New York attorney general accused the operator of bitcoin exchange Bitfinex and tether issuer Tether Limited of hiding an $850 million loss.

The state's top lawyer alleges Bitfinex used at least $700 million from Tether's cash reserves to cover up the apparent loss of $850 million of client and corporate funds. Its findings were detailed in papers filed with the Manhattan Supreme Court.

Tether is a cryptocurrency that is meant to be pegged to the U.S. dollar — otherwise known as a stablecoin. Worries have been raised over whether Tether Limited holds enough dollars to back all the tokens in circulation.

The price of bitcoin, the world's largest cryptocurrency, has fallen 4% over the last 24 hours, according to industry website CoinDesk. In the same time period, the prices of ethereum and XRP — the world's second and third-largest virtual currencies by market value — also dropped 6% and 3%, respectively. Tether's price fell over 1%, coming off its dollar peg.

The attorney general's office said Thursday that Bitfinex handed $850 million to a Panama entity called Crypto Capital without disclosing it to investors. Executives at Bitfinex and Tether then allegedly "engaged in a series of conflicted corporate transactions" — where Bitfinex gave itself access to Tether's cash reserves.