The European Union (EU) on Thursday imposed sanctions on six hackers and three groups behind some of the most significant and wide-reaching international cyberattacks in history.

The EU froze the assets and imposed a travel ban on individuals involved in the “WannaCry,” “NotPetya,” and “Operation Cloud Hopper” attacks, along with those responsible for a cyberattack against the Dutch Organization for the Prohibition of Chemical Weapons (OPCW), an intergovernmental group based in The Hague.

The 2017 WannaCry and NotPetya attacks were some of the most devastating ransomware attacks in history.

North Korean group Chosun Expo was sanctioned by the EU for involvement in the WannaCry attack, which encrypted or locked down over hundreds of thousands of computer systems across 150 countries, seriously impacting the United Kingdom’s general medical practices and targeting companies including Sony Pictures Entertainment and the Polish Financial Supervision Authority.

The NotPetya ransomware attack targeted Ukrainian and other international companies, with the attack successfully switching off parts of the Ukrainian power grid in the middle of winter.

The CIA attributed the attack to the GRU, Russia’s military intelligence agency, with the GRU’s Main Center for Technologies one of the groups sanctioned by the EU on Thursday due to the attack.

Chinese nationals Gao Qiang and Zhang Shilong, along with the Tianjin Huaying Haitai Science and Technology Development Co. in China, were sanctioned for carrying out Operation Cloud Hopper.