Fans of bitcoin are holding their breath: America’s Securities and Exchange Commission will decide today whether to allow trading in an exchange-traded fund based on the crypto-currency. A nod from the SEC would make it much easier for small traders and institutions to invest in bitcoin, and would probably boost the exchange rate, which has recently reached all-time highs of more than $1,250. Conversely, if the agency says no, expect a plunge. The decision will conclude a nearly four-year-old mission of two investors who want to start a bitcoin ETF: Cameron and Tyler Winklevoss—the twins who sued Mark Zuckerberg, Facebook’s founder, alleging that he stole the idea for the social network from them. That their crusade took so long is mainly because bitcoin is not an easy fit for an ETF, being neither a real currency nor a commodity such as gold. And taxonomy aside, it remains unclear whether bitcoin is secure enough.