British Home Secretary Amber Rudd said that Friday's cyber attack has affected 48 of the 248 NHS trusts in England, with all but six now back to normal.
Rudd said that all A&E departments are operating as normal, after chairing a meeting of Cobra, the government's emergency response committee, on Saturday afternoon, reports the Guardian.
A fifth of the trusts were hit by the ransomware on Friday afternoon, forcing hospitals to cancel and delay treatment.
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.
The Home Secretary admitted that outdated software left some NHS systems vulnerable, adding that it is important to remember that it was not the health service alone that has been affected.
"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," Rudd 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," she added.
NHS Digital said engineers are working "around the clock" to fix the problem.
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