Venture capitalists and entrepreneurs have been lobbying federal regulators to protect at least some virtual currencies from being categorized as securities, a designation that would carry significantly more oversight. The venture capital firm Andreessen Horowitz helped assemble a group of investors and lawyers that met with the Securities and Exchange Commission in late March. They also proposed a "safe harbor" for some virtual currencies, according to a copy of the proposal reviewed by The New York Times and three people briefed on the effort who agreed to speak on the condition of anonymity because the proceedings were confidential.