Bitcoin prices continued to slide early Tuesday, bringing their dive over the last 24 hours to 16 percent. The plunge came after Treasury Secretary Janet Yellen on Monday expressed concerns about the use of the cryptocurrency, calling it highly speculative, and an "inefficient" way to conduction transactions. She also said she fears it's often used for illegal activity. "People should beware it can be extremely volatile and I do worry about potential losses that investors could suffer," Yellen said at a New York Times Dealbook conference. The comments were the latest indication that Yellen's department would look into bitcoin and its use to protect investors. Yellen has hinted that more regulation could be coming for digital currencies.

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