A hacker that claims to have compromised sensitive data belonging to South Korea’s power plants has threatened to share the information with other countries if a ransom is not paid.

The unknown attacker released some information related to the power plants via Twitter on Thursday, however, the state-run Korea Hydro & Nuclear Power Co. (KHNP) believes it did not include sensitive data because the hack would have been done after the company’s recent boost in data security practices made sensitive information unreachable, according to The Korea Times. The servers used to operate nuclear reactors were cut off from outside access.

Safety protocol’s set up by KHNP don’t allow the company to open any of the documents released so they’re limited in analyzing their sensitivity.

The hacker has previously asked the organization to shut down some of the company’s nuclear reactors.