Individuals and organisations were discouraged from paying the ransom, as it was not guaranteed that the access would be restored.
MalwareTech, who wants to remain anonymous, was hailed as an “accidental hero” after registering a domain name to track the spread of the virus, which actually ended up halting it.
Investigators are working to track down those responsible for the ransomware used on Friday, known as Wanna Decryptor or WannaCry.
The virus exploits a vulnerability in Microsoft Windows software, first identified by the US National Security Agency.
A security update was released by Microsoft in March to protect against the virus.
However, it seems that many NHS trusts had not applied it or were using an older version of the operating system which is no longer supported – Windows XP.
NHS Digital said that 4.7 per cent of devices within the NHS use Windows XP, with the figure continuing to decrease.
Microsoft has now sent out patches for WindowsXP in an attempt to limit the damage, while the NHS took steps over the weekend to send out the recent security updates for trusts who had not put it in place.
The hackers are believed to have used “cyber weapons” stolen from the US’ National Security Agency to lock up computers and hold users’ files for ransom.
The most disruptive attacks were reported in the UK, where hospitals and clinics were forced to turn away patients after losing access to computers.
The ransomware is a type of malicious software that infects a computer and restricts users’ access to it until a ransom is paid to unlock it. It demands users pay USD 300 worth of cryptocurrency Bitcoin to retrieve their files, though it warns that the payment will be raised after a certain amount of time. The malware spreads through e-mail.
An Indian-origin doctor based in London had warned against the cyber-hack of the NHS just days before it crippled the country’s network.
Dr Krishna Chinthapalli, a neurology registrar at the National Hospital for Neurology and Neurosurgery in London, had warned that an increasing number of hospitals could be shut down by ransomeware attacks in an article on the vulnerability of the NHS network in the ‘British Medical Journal’ on Wednesday, two days before the major cyber-hack.
He had highlighted an incident at Papworth Hospital near Cambridge where a nurse clicked on a malicious link and malware infected her computer and started to encrypt sensitive files.