Other targets include some Asian university networks, the German transportation system, and the Spanish telecom company Telefonica.
UK Home Secretary Amber Rudd and health secretary Jeremy Hunt are holding a meeting of the country's emergency response committee, COBRA, to assess further action.
This is ironic that NHS software is stolen and used against patients, businesses and hospitals.
Meanwhile, an executive at a cybersecurity firm that helped block Friday's attack said that new variations of the malicious worm are circulating - and that researchers expect one to develop that can not be stopped.More news: US officials criticize Turkey after attack on DC protesters
"As our hospitals are still experiencing some delays and disruption, we would ask the public to use other NHS services wherever possible".
Over the weekend, the ransomware has hit systems in more than 150 countries, including Russian Federation and the United Kingdom, in one of the most widespread cyber attacks in history. Thus, governments and cyber-security forces should treat it as a "wake-up call".
There are fears of further "ransomware" attacks as people return to work on Monday.
Russian Federation and Britain were among the worst-hit countries by the attack.More news: Kushner Hands-on Broker of $110B Saudi Arms Deal
In its latest update on the incident, Europol said it was the "largest ransomware attack observed in history".
NHS Grampian said it remains "completely confident" no patient data was accessed in the ransomware attack, which hit 13 health boards across the country and countless nationwide, leaving some with a backlog of postponed appointments to contend with.
One particular vulnerability in Windows, leaked by a shady crew called Shadow Brokers, was used by the WannaCry hackers to give their ransomware a worm feature, allowing it to spread between vulnerable PCs silently and at speed. For consumers it is usually the problem of expensive mobile data which drives people to just keep Windows updates turned off altogether. The attack is taking advantage of a vulnerability in computers running Microsoft Windows.
In Zimbabwe, many Windows computers stay unpatched. It locks down all the files on an infected computer. The virus also affected many hospitals and transportation networks across Europe.More news: Sunderland goalkeeper can succeed De Gea says Manchester United legend
A 22-year-old IT researcher from a seaside town in England, Marcus Hutchins, has been credited with saving more than 100,000 computers from being affected by the malicious software after he registered a website domain name which inadvertently stopped its spread with a so-called "kill switch".
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