The news hitting that has sent cryptocurrencies plummeting is here:

In brief the allegations are that iFinex (operators of the Bitfinex cryptocurrency exchange and owns Tether) covered up missing funds, dating back to the middle of 2018. That the firm commingled client and corporate funds. The events had not been disclosed publicly.

The New York attorney general's office says it has obtained court orders requiring 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 amount involved in the alleged coverup is a drain of at least $700 million from Tether's reserves, says the NY AG.

BTC has dropped (posted a chart here as it was falling but its a lot lower now).

Also, check out Tether's USDT token … also down sharply indeed:

cryptocurrency price tether USDT drop 26 April 2019

While I'm at it, update to the earlier BTC chart:

cryptocurrency bitcoin drop on bitfinex tether news