The founding PayPal CEO believes there is “no store value” in Bitcoin and it should “not be accepted as a means of payment” and has no intrinsic value.
Writing in Recode, Mr Harris said: “Okay, I’ll say it: Bitcoin is a scam.
“In my opinion, it’s a colossal pump-and-dump scheme, the likes of which the world has never seen.
“In a pump-and-dump game, promoters “pump” up the price of a security creating a speculative frenzy, then “dump” some of their holdings at artificially high prices.
“And some cryptocurrencies are pure frauds.”
Mr Harris explained his reasoning and said Bitcoin cannot be accepted as a means of payment. He told CNBC: “Even in emerging markets, they might as well use dollars, euros or existing currencies if the local currency is subject to hyperinflation.”
But the businessman admitted there is “a lot” about Bitcoin that is “not a scam”.
He added: “But yes, everyone is drinking the kool-aid. Just a couple of days ago somebody relatively prominent said Bitcoin is bigger than the internet, bigger than the industrial revolution. Seriously.
He added: “He’s also said that in four years it’ll appreciate to the point where Bitcoin and all cryptocurrencies will be worth about half of the entire S&P 500.
“There’s just no relation between value and usefulness. And on the usefulness side, let me just – there’s the currency like Bitcoin and then there’s the technology like blockchain.
“Blockchain technology has terrific applications including financial transactions. But we don’t need a new currency to do it. And, by the way, there’s no reason that a new currency should instantly have billions of dollars of value.”
Bitcoin price was at $9,340.26 at 11:20 (GMT) on Friday, according to CoinDesk. It saw its highest value before Christmas when it reached the monumental price of just under $20,000.
The digital currency has faced a mixed response with Twitter co-founder and CEO Jack Dorsey predicting Bitcoin will soon be the single online currency.
Mr Dorsey said: “The world ultimately will have a single currency, the internet will have a single currency. I personally believe that it will be Bitcoin.”
Hedge fund manager John Pfeffer also said Bitcoin could continue to surge by “hundreds of thousands” if it replaces a major reserve currency.
Speaking at the Sohn Investment Conference, the cryptocurrency expert predicted that Bitcoin will rise to no less than $90,000 and potentially as high as $700,000.
Mr Pfeffer told CNBC: “The bear case is zero. I think people should think about crypto assets, Bitcoin, as a venture capital investment. It could go to zero but there’s a chance that they could be worth much more.
“And the case of Bitcoin, the $90,000 price would be what it would be worth if Bitcoin became equal to private gold bullion holdings, about 1.6 trillion dollars of total value compared to $150 billion or there about today.
“It’s a bet. It’s a risk that I think is interesting and I’d be willing to take.”