Investing.com - The massive rally in cryptocurrency prices during 2017 was stunning to some and suspicious to others. A new study supports those suspicions, alleging that at least half of the gains of bitcoin and other digital currencies was the result of coordinated price manipulation.The study by two scholars at the University of Texas says that transaction records show another digital coin, Tether, was frequently used to purchase bitcoin during market downturns, which ultimately boosted its price. Other currencies were similarly affected .The study singles out trading on the Bitfinex exchange, which created and issued Tether, but the suspicious activity took place on other exchanges as well.Bitfinex responded to the study, saying it has not "engaged in any sort of market or price manipulation."Bitcoin soared to almost $20,000 in 2017, but has been on a downward spiral almost ever since.