Veteran investor and IAC chairman Barry Diller said Friday that he didn’t trust cryptocurrencies and believes that the digital assets are “a con.”

“I watch some of the people that you have on and they talk about it – $40,000, $12,000, whatever – I think ‘this is nutso talk,'” Diller said CNBC’s “Squawk Box” after originally indicating he didn’t want to talk about the crypto space.

Diller’s comments come after a volatile week in the cryptocurrency world, in which a major sell-off on Tuesday and Wednesday dragged the price of bitcoin down more than 30% to $30,000 at one point before stabilizing near $40,000. Other crypto assets, including ether and dogecoin, also declined.

The dramatic sell-off comes amid increased worry about regulation from the U.S. and China and environmental issues around bitcoin, highlighted by Tesla CEO Elon Musk.

Cryptocurrencies had surged in price over the past year as big name investors and institutions began to embrace the new asset class, in particular bitcoin and ether. However, the rise of less serious versions like dogecoin, along with volatile moves in stocks like GameStop that gained traction on social media, have fueled concerns about speculation in financial markets.

This week’s round of volatility is not uncommon for the crypto space. In late 2017, bitcoin peaked above $19,000 before pulling back sharply, eventually losing about 80% of its value over a 12-month period.

Many crypto bulls argue that bitcoin’s decentralized nature and limited circulation, along with its newfound institutional backing, can help it develop a role as a store of value. Hedge fund veteran Stanley Druckenmiller said earlier this month that a potential dominant cryptocurrency for everyday commerce likely hasn’t been invented yet.

In the early afternoon on Friday, bitcoin was trading at just over $37,000, according to Coin Metrics.