The US securities regulator has warned that cryptocurrency exchanges risk operating illegally because they do not make disclosures about how they prioritise investors' orders or pick tokens that trade on their venues, Dave Michaels writes for The Wall Street Journal.

The investor alert from the Securities and Exchange Commission is its latest effort to regulate the multibillion-dollar US market for raising funds in virtual currencies. The watchdog has said many tokens issued through initial coin offerings are securities, and has issued more than 100 information requests and subpoenas to firms and advisers operating in the market.