- Video report by ITV News Correspondent Richard Pallot
International efforts are under way to track down the perpetrators behind a cyber attack which threw the NHS into chaos and affected businesses across the world.
On Sunday evening seven hospitals were said to still be affected by the attack.
Europol, the EU's police agency, has said there have been more than 200,000 victims - including the NHS - across at least 150 countries, and there are fears that many more people may be hit by the virus on Monday when they return to work.
Speaking on ITV's Peston on Sunday, Europol director Rob Wainwright warned that "all sectors" were vulnerable to attack and urged organisations to ensure they updated their systems.
He continued: "At the moment we are in the face of an escalating threat, the numbers are going up, I am worried about how the numbers will continue to grow when people go to work and turn their machines on Monday morning.
"The latest count is over 200,000 victims in at least 150 countries. Many of those will be businesses including large corporations."
At this time the identity of the attackers who deployed the ransomware bug remains unknown.
But Europol said its cybercrime specialists had begun a "complex international investigation" to identify the culprits.
And Oliver Gower from the National Crime Agency, said: "Cyber criminals may believe they are anonymous but we will use all the tools at our disposal to bring them to justice."
Europol said the current challenge was the fast-spreading capabilities of the malware, which locks up data and demands a payment for it to be released.
However, it appears that few have paid the ransom the software demands.
Meanwhile a British cyber security researcher known online as MalwareTech has warned that another attack could come as soon as Monday.
He was hailed an "accidental hero" after helping prevent the virus from spreading further when he and another researcher stumbled upon a "kill switch" in the malware code.
The 22-year-old said: "We have stopped this one, but there will be another one coming and it will not be stoppable by us.
"There's a lot of money in this. There's no reason for them to stop. It's not really much effort for them to change the code and then start over.
The NHS systems are believed to have been hit by a ransomware cyber attack using malware called "Wanna Decryptor".
The attack that began on Friday is believed to be the biggest online extortion attack ever recorded, disrupting computers that run factories, banks, government agencies and transport systems.
The NHS fell victim to the attack with 48 trusts in England and 13 health boards in Scotland affected by the ransomware, leading to the cancellation of operations and appointments across the country.
Medical staff reported seeing computers go down "one by one" as the attack took hold, locking machines and demanding money to release the data.
Health authorities are now racing to upgrade security software amid fears hackers could exploit the same vulnerability with a new virus.
There have been calls for an inquiry into the circumstances surrounding Friday's major incident, with the government and NHS chiefs facing questions over their preparedness and the robustness of vital systems.
On Saturday a former head of the body managing the NHS' cyber security system said an online attack on the health service was "always going to happen".
He said although the government has invested in protecting against a cyber attack, it can be "difficult" to ensure trusts spend money on cyber security.
Speaking after a Cobra meeting on Saturday, Home Secretary Amber Rudd admitted "there's always more" that can be done to protect against cyber attacks.
But she stressed that attack had affected organisations in scores of countries.
"If you look at who's been impacted by this virus, it's a huge variety across different industries and across international governments. This is a virus that attacked Windows platforms. The fact is the NHS has fallen victim to this," she said.
"I don't think it's to do with that preparedness. There's always more we can all do to make sure we're secure against viruses, but I think there have already been good preparations in place by the NHS to make sure they were ready for this sort of attack."
NHS Digital, which manages the health service cyber security, said fewer than 5 percent of devices within the health service still use the old Windows XP system.
Nissan UK confirmed it was affected, but said there had been "no major impact".
It is understood its plant in Sunderland is not due to have another production shift until Sunday night.
A spokesman said: "Like many organisations around the world, some Nissan entities were recently targeted by a ransomware attack.
"Our teams are responding accordingly and there has been no major impact on our business. We are continuing to monitor the situation."