A young British computer expert hailed a hero for helping to shut down the crippling cyber attack said he was just "doing my bit" to stop the hackers.
Marcus Hutchins, 22, discovered a so-called "kill switch" that slowed the effects of the WannaCry virus as it swept through computer systems around the world.
Large swathes of the NHS were paralysed by the cyber attack, which hit 200,000 victims in 150 countries around the world.
But Mr Hutchins, who works for Los Angeles-based Kryptos Logic but is from Ilfracombe in north Devon, spent the weekend fighting against the virus that meant computer systems were able to return to relative normality.
He told the Associated Press: "I'm definitely not a hero. I'm just someone doing my bit to stop botnets."
It came as the former head of Britain's eavesdropping service has hit out at Microsoft for failing to protect vulnerable computer systems affected by the crippling ransomware attack.
Sir David Omand, the former head of GCHQ who was once homeland security adviser to Number 10, said the tech giant knew public bodies around the world were at risk from hackers.
In a letter to The Times, Sir David said: "Should Microsoft have stopped supporting Windows XP so soon, knowing that institutions had invested heavily in it (at the urging of the company at the time)?"
Home Secretary Amber Rudd said the NHS was "open for business", with only a handful of hospitals still suffering disruption caused by Friday's hack.
Following a meeting of the Government's Cobra contingencies committee, Ms Rudd said more than a million patients had been treated in the course of Monday.
"All GPs surgeries did open, though some of them had to use pen and paper," she said.
"The vast majority of patients have noticed no difference. It has been a very strong response."
Earlier on Monday, Health Secretary Jeremy Hunt confirmed there had not been a second wave of attacks on NHS trusts and said it was "encouraging" that the level of criminal activity was at "the lower end of the range" anticipated.
Mr Hunt has come under fire for failing to appear in public since the attack, which hit 47 trusts in England and 13 Scottish health boards.
In his first public comments since the attack, Mr Hunt told Sky News: "Although we have never seen anything on this scale when it comes to ransomware attacks, they are relatively common and there are things that you can do, that everyone can do, all of us can do, to protect ourselves against them.
"In particular, making sure that our data is properly backed up and making sure that we are using the software patches, the anti-virus patches, that are sent out regularly by manufacturers."
NHS Digital said health trusts across England were sent details of an IT security patch that would have protected them from the attack.
The health service has been criticised for using the outdated Windows XP operating system to store digital information, despite security updates for the software having been discontinued by Microsoft.
NHS Digital said it had made health trusts aware last month of IT protection that could have prevented the damage.