The step was taken because the exchange "facilitated transactions involving illicit proceeds from at least eight ransomware variants," a statement by the Treasury Department said.

The U.S. Treasury Department announced this week a series of actions aimed at disrupting malicious cyber groups behind ransomware attacks, while encouraging better cybersecurity in the private sector and extensive cooperation between government agencies and the various companies as part of the government's broader counter-ransomware strategy. The first action was imposition of sanctions on Russian cryptocurrency exchange SUEX. 

According to the Treasury Department's statement, SUEX "has facilitated transactions involving illicit proceeds from at least eight ransomware variants. Analysis of known SUEX transactions shows that over 40% of SUEX’s known transaction history is associated with illicit actors." Under the sanctions, all property and interests in property in territories subject to U.S. jurisdiction are blocked, and both U.S. citizens and organizations are prohibited from engaging in transactions with the exchange. 

"Ransomware and cyber-attacks are victimizing businesses large and small across America and are a direct threat to our economy," said Treasury Secretary Janet Yellen in the statement released on the department's website. "As cyber criminals use increasingly sophisticated methods and technology, we are committed to using the full range of measures, to include sanctions and regulatory tools, to disrupt, deter, and prevent ransomware attacks."