Earlier this year, several employees at a nuclear power plant in southern Ukraine connected part of the internal network to the Internet in order to mine cryptocurrency, authorities said. The Ukrainian Secret Service (SBU) is investigating the incident to check if attackers may have used the Internet-facing mining rigs (computers set up to mine crypto) in order to breach the power plant’s network and obtain access to confidential data about the facility.

After the SBU learned about the scheme, it raided the power plant in July and confiscated several mining rigs and related equipment. A number of employees have been charged for participating in the scheme that could be considered a threat to national security if critical infrastructure and state secrets were put at risk.

Read more: Employees connect nuclear plant to the internet so they can mine cryptocurrency