Academic researchers at the University of Texas have concluded at least half of Bitcoin’s rise to a peak price of nearly $20,000 last year was due to manipulation by traders on Bitfinex, the primary Bitcoin exchange, using another cryptocurrency called Tether to boost prices when they dipped on other exchanges.

The paper by John Griffin, a finance professor at the University of Texas, and graduate student Amin Shams, examined trading between March 2017 and March 2018 with particular focus on 87 periods each lasting one hour when Tether, which is issued exclusively by Bitfinex, flowed onto other exchanges when the price of Bitcoin was dropping. “These 87 events account for less than 1 percent of our time series (over the period from the beginning of March 2017 to the end of March 2018), yet are associated with 50 percent of Bitcoin’s compounded return, and 64 percent of the returns on six other large cryptocurrencies (Dash, Ethereum Classic, Ethereum, Litecoin, Monero and Zcash),” the researchers wrote.

The researchers ran 10,000 trading simulations and concluded “this behavior never occurs randomly.”

“There were obviously tremendous price increases last year, and this paper indicates that manipulation played a large part in those price increases,” Griffin told the New York Times, where the paper was first reported.

Trading on Bitfinex, which is registered in the Caribbean with offices in Asia, is largely unregulated by any government. Bitfinex CEO JL van der Velde denied any wrongdoing in a statement to Business Insider. “Bitfinex nor Tether is, or has ever, engaged in any sort of market or price manipulation. Tether issuances cannot be used to prop up the price of Bitcoin or any other coin/token on Bitfinex,” van der Velde said.

The researchers noted cryptocurrencies bear a striking similarity to well-researched investment bubbles stretching from the 18th century to the dot.com and housing crashes of recent years. “Cryptocurrencies, which have grown from nearly nothing to over $300 billion in market capitalization in a few years, fit the historical narrative of previous bubbles quite well — there is an innovative technology with extreme speculation surrounding it.”

The historical pattern the researchers allude to stretches back centuries. While the assets change — the scam remains remarkably similiar. “Periods of excessive price speculation often share the themes of optimism around a new technology, focusing on selling to others rather than economic fundamentals, and questionable activities,” the researchers wrote. They cited the South Sea Bubble 1719-1720 and Railroad Bubble of the 1840s as early examples of investors being stampeded into buying stock in an unregulated investment based on false claims and pure exuberance.

While the lack of regulation by any government appeals to some cryptocurrency enthusiasts, the authors of the research suggest only regulation can stabilize crypto markets. “Our findings suggest that market surveillance within a proper regulatory framework may be needed for cryptocurrency markets to be legitimate stores of value and a reliable medium for fair financial transactions,” they wrote.

Bitcoin was trading below $6,500 after the publishing of the New York Times article.