WASHINGTON - The irrepressible Winklevoss twins, known for having sued Mark Zuckerberg over the idea for Facebook (FB), have suffered a setback from federal regulators in their push to expand the use of bitcoin to a wider universe of investors.

The Securities and Exchange Commission rejected Friday a proposed Winklevoss exchange-traded fund that could have opened the digital currency to larger numbers of ordinary investors. The SEC said the proposal from Tyler and Cameron Winklevoss was inconsistent with rules for securities exchanges designed to prevent fraud and manipulation, and to protect investors.

Bitcoin allows people to buy goods and services and exchange money without involving banks, credit card issuers or other third parties. About 8 years old, it has yet to be broadly embraced and has been prone to wild price swings.