Starting in June, Google (GOOG) will no longer accept advertising for cryptocurrencies and initial coin offerings, part of a larger effort to restrict the marketing of financial offerings viewed as .
Twitter has also said it's acting to curb crypto-related spam.
Cryptocurrencies swooned across the board following Google's announcement. Bitcoin, the biggest in terms of market valuation, was lately down 4.5 percent. Competitors including Ethereum and Ripple both declined more than 5 percent.
As the two biggest sellers of online ads distance themselves from bitcoin and other crypto assets, regulators are bearing down on them. The U.S. Securities and Exchange Commission last week reiterated a warning that some digital-coin trading platforms might be breaking the law by not registering with the agency.
Google's policy change came along with its release of an annual accounting of the deceptive and malicious ads that the company scrubs from its online network. Last year, Google cleared 3.2 billion ads from the web, up from 1.7 billion in 2016, it said.