Six NHS trusts are yet to return to normal around 24 hours after an international cyber attack struck computer systems across the globe.
Speaking after an emergency meeting, Home Secretary Amber Rudd acknowledged "there's always more" that can be done to protect against viruses.
A fifth of trusts were hit by the ransomware on Friday afternoon, forcing hospitals to cancel and delay treatment.
Ms Rudd said: "Of the 48 that have been impacted, most of them are back to normal course of business.
"So only six of them have some limits on their business."
Experts have been working to disrupt the unprecedented attack, which is thought to have affected industries across 100 countries, including the US and Russia.
A Nissan UK spokesman 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.
Amid suggestions outdated software left some health service systems vulnerable after a security package was stopped in 2015, Ms Rudd said it is important to remember the NHS alone had not been affected.
She said: "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.
"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."
Medical staff had reported seeing computers go down "one by one" as the attack took hold, locking machines and demanding money to release the data.
Paying tribute to those who worked to limit the impact, Ms Rudd said: "We've talked about how we can make sure the NHS can remain robust, that patients come first, and I'd like to commend the work that NHS staff have done to ensure that hospitals and patient surgeries are going to continue to run smoothly.
"The fact 97% of the NHS trusts and hospitals and doctors are working as normal, so the response has in fact been very good and that's due to the good work of the staff and the resilience that was already put in place."
The virus, called Wanna Decryptor, exploits a vulnerability in Microsoft Windows software first identified by American spies at the National Security Agency (NSA), experts have said.
Computers in A&E wards, GP surgeries and other vital services were thought to have been infected with the virus.
They were infiltrated by the malicious software, while many others shut down servers as a precautionary measure.
Shadow health secretary Jonathan Ashworth, in a letter to Health Secretary Jeremy Hunt, said concerns were repeatedly flagged about outdated computer systems.
Responding earlier, Ms Rudd said: "This Government has long recognised the growing threat of cyber attack from those who wish to do us harm and has invested significantly to bolster our cyber defences."
Labour leader Jeremy Corbyn branded the attackers "a bunch of 21st century highway robbers" and expressed anger that the Government did not renew a multimillion-pound security package.
He said: "It's unbelievably disgusting and I've got nothing but contempt for those people that have done it, and I'm sure all of you would share that.
"But I'm also very angry that in 2014, there was a one-year renewal of the protection system on the NHS systems which was not renewed after that and not renewed the year after that and so systems are now not upgraded and not protected.
"As a result, we've got this dreadful situation that NHS workers are facing today."
Just one day before Friday's attack a doctor warned that NHS hospitals needed to be prepared for an incident precisely of the kind seen.
In an article published in the British Medical Journal, Dr Krishna Chinthapalli, a neurology registrar at the National Hospital for Neurology and Neurosurgery in London, said hospitals "will almost certainly be shut down by ransomware this year".
A spokesman for Nissan UK 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."
NHS Digital, which manages health service cyber security, said fewer than 5% of devices within the health service still use the old system Windows XP.
A spokesman said: "We are aware of widespread speculation about the use of Microsoft Windows XP by NHS organisations, who commission IT systems locally depending on population need.
"While the vast majority are running contemporary systems, we can confirm that the number of devices within the NHS that reportedly use XP has fallen to 4.7%, with this figure continuing to decrease.
"This may be because some expensive hardware (such as MRI scanners) cannot be updated immediately, and in such instances organisations will take steps to mitigate any risk, such as by isolating the device from the main network."
He added that they would not publish a list of the remaining affected organisations.
Only health organisations in England and Scotland were affected by the attack.