Europol executive director Rob Wainwright said the situation could worsen on Monday when workers return to their offices after the weekend and log on. The so-called WannaCry Ransomware attack targets vulnerable Windows operating systems in mostly Europe and Asia, though some North American businesses and users were also affected.
'It's an global attack and a number of countries and organisations have been affected, ' British Prime Minister Theresa May said.
Last night, she said: "The concern is that on Monday morning the appointment system may not be working, some places may not be able to access routine results, even the phone lines in some cases may not be working".
The source says that thanks to the information published by local media, citizens are on the alert about the existence of the virus to help contain the spreading of the world cyber-attack.
A global cyberattack second wave was awaited Monday morning as employees in about 150 countries went back to work braced for aftershocks of Friday's attack, being referred to as the worst "online extortion" ever.
Eleven health boards as well as NHS National Services and the Scottish Ambulance Service were affected in the unprecedented cyber attack which hit scores of countries on Friday.More news: President Trump breaks from predecessors, doesn't host Cinco de Mayo celebration
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However there was disruption to the x-ray service.
Cyber Security Minister Dan Tehan said on Sunday the government received reports of the private sector being impacted, but not commonwealth organisations.
The virus exploits a vulnerability in Microsoft Windows software, first identified by the US National Security Agency.
"We would like to extend our thanks to our staff for the hard work they have done to ensure patient care has been prioritised during this difficult time, and to our patients for their understanding".
The PSNI said it was working with national and worldwide law enforcement agencies to reduce any risk to computer networks in Northern Ireland.