'200000 users, 150 countries hit by ransomware'

But computers and networks that hadn't updated their systems were still at risk.

An unprecedented "ransomware" cyberattack that has already hit tens of thousands of victims in 150 countries could wreak greater havoc as more malicious variations appear and people return to their desks Monday and power up computers at the start of the workweek.

"We are in the face of an escalating threat", Wainwright added.

Cyber security experts say the spread of the virus dubbed WannaCry - "ransomware" which locked up computers in vehicle factories, hospitals, shops and schools in several countries - has slowed, but that any respite might be brief.

They advised those whose networks have been effectively shut down by the ransomware attack not to make the payment demanded - the equivalent of $300, paid in the digital currency bitcoin, delivered to a likely untraceable destination that consists merely of a lengthy string of letters and numbers. Russian Federation and Ukraine had a heavy concentration of infections, according to Dutch security company Avast Software BV.

U.S. Treasury Secretary Steven Mnuchin, at a meeting of world leaders in Italy, said the attack was a reminder of the importance of cybersecurity.

Mr Hunt has not publicly responded to the attack, but Home Secretary Amber Rudd said the priority was to "disrupt" it.

Microsoft was quick to change its policy, announcing free security patches to fix this vulnerability in the older Windows systems still used by millions of individuals and smaller businesses.

It comes amid concerns NHS networks were left vulnerable because they were still using outdated Windows XP software.

Wainwright's televised comments followed a statement Saturday in which Europol cited the unprecedented scale of the attack and said that its European Cybercrime Center, known as EC3, was "working closely with affected countries cybercrime units and key industry partners to mitigate the threat and assist victims". "Most of the reported cases of payment of ransom are from overseas". Hospitals are also fertile ground for identity thieves due to their often-lax security policies.

Attacks on hospital data and patients were "despicable at the basic level", he said.

Mumbai: Globally active ransomware virus has partially affected the computer systems in some institutions in Maharashtra, including that of its police department, a police official said here on Sunday.

"Report such instances of fraud to CERT-In and law enforcement agencies", it said.

A display panel with the attack running can be seen Friday at the main railway station in Chemnitz, Germany.

The student said his computer was infected after logging onto his Facebook account, which showed a garbled message that led to the activation of the ransomware, according to local police. Indonesia's government reported two hospitals in Jakarta were affected.

Ransomware is a particularly stubborn problem because victims are often tricked into allowing the malicious software to run on their computers, and the encryption happens too fast for security software to catch it.

The threat from the cyber attack that crippled worldwide services "will continue to grow" as people return to work on Monday, the head of Europol warned. The attack was apparently halted in the afternoon in the United Kingdom when a researcher took control of an Internet domain that acted as a kill switch for the worm's propagation, according to Ars Technica.

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.

Instead he suggested hackers unnconnected to the ransomware attacks may have been trying to pull off a feat that would give them a degree of "fame".

Computer users worldwide - and everyone else who depends on them - should assume that the next big "ransomware" attack has already been launched, and just hasn't manifested itself yet, said Ori Eisen, founder of the Trusona cybersecurity firm in Scottsdale, Arizona.