Ok not legally a "currency" according to the IRS, but still a product, rather than a share in a company or a bond.

The SEC doesn't get involved in Farmville plots of land, any more than it gets involved in physical real estate. It's not involved if I sell you a gold coin or rare stamp, even if you hope to resell at a profit.

Cryptocurrencies seem more analogous to these things, rather than equities, debts, profit-sharing agreements, or anything else in the SEC's official definition of a security:

http://www.thestreet.com/topic/47042/securities.html