Micheál Martin, the Taoiseach, said cybersecurity experts would deal with the matter ‘methodically’ and no money would be paid after ransomware infected the Health Service Executive (HSE) computer systems.
Ransomware typically shuts down core IT functions and forces users to pay money to unlock them again.
The hack is ‘possibly the most significant cybercrime attack on the Irish state’, a minister said on Friday.
The state’s IT services were shut down after the attack, although the HSE said on Twitter this was a temporary ‘precaution’.
Mr Martin’s deputy, former Taoiseach Leo Varadkar, said it could affect systems for several days to come.
While emergency services, GPs and pharmacies have been spared from any impact, he warned of ‘major problems’ for services including cancer treatments, radiology and elective surgery.
He said: ‘It’s going to be a very difficult time for the health service.
‘There’s lots we don’t know but it appears to be a ransomware attack by international criminals.
‘The problem could run through the weekend and into next week, unfortunately.’
Chief medical officer Dr Tony Holohan warned of disruption to Covid test appointment booking systems, although people can still get tested at walk-in centres.
Mr Martin added: ‘This is something that has to be dealt with in a methodical way. The system has been shut down. There’s an assessment under way, identification of the issues and other processes.
‘It will take some days to assess the impact and that is the proper way to do this and we will make those assessments over time.
‘What’s important is people co-operate with the HSE, emergency services are open, the vaccination programme continues uninterrupted.
‘At this stage we are dealing with this in accordance with the advice we’ve received from cyber security experts and I think we’re very clear we will not be paying any ransom.
‘The work continues by the experts.’