Patients at one of the UK's major hospitals affected by the cyber attack had operations cancelled as staff were ordered not to touch their computers.
Outside the Royal London Hospital, wheelchair-bound patient Richard Harvey spoke of his disappointment as he wheeled himself home after waiting all day for a procedure that was eventually postponed.
He had been fasting all day and limiting water intake ahead of the operation, he said.
The 50-year-old, who suffered injuries to his hip in a motorcycle accident three years ago, told the Press Association: "Originally I came here because my leg and pelvis kept opening, I was due today to have it washed out and stitched up again.
"I was actually in my bed most of the day, they prefer you not to get out of bed. I didn't have a time. The operation could have come at any time.
"At ten to five I said to a nurse 'this is a bit late for an operation' and she said 'there's been a cyber attack' and I said 'well go and check'.
"She went away and came back and said that was it."
He added: "I was very disappointed. I had been waiting all day.
"I was very nervous. I am quite a nervous person when it comes to things like this. I was quite disappointed and hungry.
"I would like them to come up a bit earlier and say it has been cancelled. I could have had something to drink a lot earlier."
The site's A&E department still had people entering and leaving by early evening, but they were greeted by a handwritten sign that read: "The emergency department has no IT facilities, there are significant delays occurring."
According to one member of staff, employees had been told not to go on their desktop computers after the virus infiltrated the system.
Mother Parvin Begum, 40, was surprised by the emptiness of the A&E waiting room when she visited the Royal London with her daughter on Friday afternoon.
She said: "There were only a few patients that I saw in A&E, it was really quiet."
New parents were suffering delays in being discharged from the maternity ward due to the computer systems going down, one father said.
Warren Jones saw his partner give birth to their fourth daughter, Laurie, at around 10.30am, but said nurses were unable to print identity tags to put round the wrists of newborns.
The 24-year-old courier said: "I don't know what is going on, basically they are saying nobody is going to be around today, we are ready to go home.
"They are basically saying it is full, there are so many people, it is rammed, but they don't want to let people go.
"It is normal to have two baby tags - we have got no tags. They can't print them out I'm guessing.
"It is a bit disappointing really, I don't know how easy it is but they have taken over a whole system and shut it down."
One mother, who asked not to be named, said an expected transfer for her daughter, who was in a wheelchair, to another hospital was knocked back.
She said: "My daughter has been here for three-and-a-half weeks and she was told she would be moved to another hospital which was available, but because of the cyber attack she could not be moved.
"We are just waiting and waiting, it's the uncertainty that's very frustrating and devastating really.
"I arrived to visit my daughter and I went to the nurses 'oh, I need to know, is it tonight?' and they went 'did you not hear about the cyber attack, everything is on hold'."