The ratio of legal to illegal activity in conducted in bitcoin has flipped, according to Lilita Infante at the U.S. Drug Enforcement Administration (DEA).

When Infante started seeing the bitcoin pop up in her cases at the DEA five years ago, her analysis of blockchain data showed criminal activity was behind about 90 percent of transactions in the cryptocurrency. Now, illegal activity has shrunk to about 10 percent and speculation has become the dominant driver, she said.

That doesn't mean criminals stopped using bitcoin. Total transaction volume associated with illegal uses has surged since 2013, said Infante, who is a DEA special agent and part of the 10-person Cyber Investigative Task Force. The team focuses on dark web and virtual-currency related investigations and collaborates with other Department of Justice units including the Federal Bureau of Investigation and the Bureau of Alcohol, Tobacco, Firearms and Explosives.