The total cost of a ransomware attack on the Health Service Executive could reach €100 million, the chief executive of the HSE has told an Oireachtas committee.

The HSE was forced to shut down all of its IT systems earlier this year following the "significant" ransomware attack, which focused on accessing data stored on central servers.

Speaking at the Oireachtas Public Accounts Committee, Paul Reid said the cyber attack has necessitated the replacement of 30,000 devices at a cost of about €30m.

Mr Reid told the PAC that this is a recurring cost.

He said that the immediate cost in terms of infrastructure, vendor support and monitoring is close to €20m. Costs of monitoring will also be also recurring, he added.

Mr Reid also said 512 patient records and a "whole range of corporate documentation" were recovered from one site.

However he said that there can be no certainty as to what was stolen.

The HSE has 2,000 systems and 4,000 servers, and "at least 80,000 devices", Mr Reid said.

The HSE used the vaccination programme "to get greater information on patient identifiers", which has helped the organisation hugely, he said.