Digital currencies like bitcoin and ethereum are built on a software called blockchain, which cuts out the need for a middleman. That means no banks clear your transactions.

But, "if you're a true adventurer and you really want to throw the Hail Mary," says Cuban, "you might take 10 percent [of your savings] and put it in bitcoin or ethereum."

In general, billionaire Mark Cuban advises putting your savings into "the cheapest SPX mutual fund you can find," he tells Vanity Fair .

"Some of the most well-known figures on Wall Street are starting to embrace the cryptocurrency," CNBC's Fred Imbert reports, including Fundstrat's Tom Lee and value investor Bill Miller.

One Dutch family even bet all they have on bitcoin.

Still, it's a speculative asset and prone to dramatic price swings. Tony Robbins says investing in bitcoin is "like going to Vegas."

Others aren't sold on the idea at all. JPMorgan Chase CEO Jamie Dimon called bitcoin a "fraud." "It's just not a real thing. Eventually it will be closed," he said at the Delivering Alpha conference in September presented by CNBC and Institutional Investor. "It won't end well. Someone is going to get killed."

And billionaire investor Howard Marks called it a "pyramid scheme."

That's why Cuban says that, if you bet on bitcoin, "you've got to pretend you've already lost your money. … It's a flyer, but I'd limit it to 10 percent."

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