New York's Attorney General, Eric Schneiderman, has sent letters of inquiry to 13 popular cryptocurrency exchanges, including Coinbase's GDAX and Gemini, about their operations and tools to protect customers.

Why it matters: Exchanges have been an area of concern and skepticism for regulators. Even the Securities and Exchange Commission and its chairman, Jay Clayton, have repeatedly warned that cryptocurrency exchanges aren't regulated like stock exchanges and shouldn't be trusted to operate with as much integrity.