A criminal gang based in Russia is believed by authorities to be responsible for last week’s attack, the most serious cyber attack on State infrastructure to date and likely the most serious on a health service anywhere in the world.

The ransomware attack saw HSE data frozen pending the payment of a ransom, which the government has refused to pay and is working to recover by other means. There are now fears that data may have also been stolen and could be traded online.

Health Minister Stephen Donnelly welcomed the High Court order and said it “shows how seriously myself and my colleagues in government are taking this event”.

He added: “The disgraceful cyber attack this week is an attack on the Irish State and all of us who value our health system so highly, particularly in light of the heroic response from all members of our health services in the last year.

“I am also this evening in a position to confirm that the decryption key to unlock the data has now been made available. No ransom was paid by the Irish State. We will continue to work with all parties to further the national response and fully reinstate our health services.”