The attack looks like this: images appear on victims' screens demanding payment of $300 (275 euros) in the virtual currency Bitcoin, saying: "Ooops, your files have been encrypted!"
The ransomware utilises vulnerabilities in out-of-date, unpatched versions of Microsoft Windows to infect devices.
Experts said they are working round-the-clock to restore the IT systems of NHS after they were hit by a large-scale cyber-hack by an worldwide criminal gang that wreaked havoc around the world and whose ransomware affected 99 countries over the weekend, including India.
She said: "We were instructed by the CCG to turn all computers off on Friday afternoon".
There are several factors in play.
Further victims were expected, the Prime Minister's cybersecurity adviser Alastair MacGibbon told ABC radio last night.
Wainwright said the agency is analyzing the virus and has yet to identify who is responsible for the attack.
At least one hospital was affected, according to police.
In the world of ransomware, that was "unheard of six months ago", Levy said. It said programmes were being installed to fix the problem. Adam Meyers, Vice President, Cyber Security Company at CrowdStrike commented below.More news: Trump assails 'witch hunt' after naming of special counsel
"And also existing known infections can spread".
"While Microsoft's release of back-ported patches is a commendable proactive action, the ACSC considers organisations running Windows XP, Server 2003 and other unsupported operating systems to be exposed to extreme risk", the organisation said in a statement. Moreover, up-dating system software and security programs can be more complex and costly for such entities given their sheer size, thus, exposing them to significant attacks based upon the vulnerability of their systems.
The malware can directly decrypt system files using a unique decryption key.
Russian Central Bank: State media agency Tass reported the bank discovered malware bulk emails to banks but detected no compromise of resources.
As the global cyber-attack slows, what can organisations do if a ransomware copycat strikes.
The impact of the cyberattack in Ireland is still being estimated but this morning, as HSE staff return to work, the Government has advised workers that when they switch on their machines, they must not log in for the first two hours, in order to let antivirus software do its work. In that regard, the institution called on all sectors to solve their problems in the field of cyber-security. He said the situation was under control.
Among the largest organisations to have been hit so far are the UK's National Health Service and Spanish telco Telefónica. "At this stage, we do not have any evidence that patient data has been accessed".
Railway stations, mail delivery, gas stations, hospitals, office buildings, shopping malls and government services also were affected, China's Xinhua News Agency said, citing the Threat Intelligence Center of Qihoo 360, a Chinese internet security services company.
"Everyone at the top level should have woken up to this by now because these attacks in email attachments have been going on for a long time". It is possible they will try to use other Equation/NSA exploits leaked by the Shadow Brokers or will be quicker to adopt exploits for future flaws that enable similar mass-scale attacks inside LANs.