How to protect yourself from the massive worldwide cyberattack

British Prime Minister Theresa May says a cyberattack that has crippled some United Kingdom hospitals is part of a wider global attack.

Britain's home secretary said one in five of 248 National Health Service groups had been hit.

(AP Photo/Alastair Grant, File). He said the virus attack that crippled computers worldwide proves that "stockpiling of vulnerabilities by governments" is a major problem.

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.

These hackers "have caused enormous amounts of disruption- probably the biggest ransomware cyberattack in history", said Graham Cluley, a veteran of the anti-virus industry in Oxford, England.

As a result, numerous organizations such as the U.K.'s National Health Service have found themselves unable to access vital data because their files were encrypted by the cyberattack, which demanded ransom payments in the Bitcoin digital currency to unlock information.

In a blog post, the US tech giant recalled that it had published an update in March to address the weakness exploited in Friday's attacks, a security flaw exposed in documents leaked from the US National Security Agency. They asked patients not to come to the hospitals unless it was an emergency.

As not all ransomware provides this timer countdown, said the team, the WannaCry attack shows computer users that "payment will be raised" after a specific countdown, along with another display raising urgency to pay up, threatening that the user will completely lose their files after the set timeout. Though the governments and companies have been able to gain the upper hand, the ransomware could be back in a big way. Don't click on links that you don't recognize, or download files from people you don't know personally.

"Affected machines have six hours to pay up and every few hours the ransom goes up", Kurt Baumgartner, the principal security researcher at Kaspersky Lab, told CNN.

The attack in Britain had immediate impacts in hospitals across the country.

"That's what makes this more troubling than ransomware was a week ago", Thakur said.

Microsoft issued a security update on March 14 about vulnerabilities in the Windows system.

By Kaspersky Lab's count, the malware struck at least 74 countries.

That's why companies are anxious to beef up security or combat potential infections, according to Aviv Grafi, the chief technology officer of Votiro, another cybersecurity firm. Once it gets into your computer, it looks for the other computers on the network to spread itself as widely as possible.

Similar widespread attacks have been reported in Spain and other countries.

Patrick Ward, a 47-year-old sales director, said his heart operation, scheduled for Friday, was canceled at St. Bartholomew's Hospital in London. Using a particular NSA hacking tool called EternalBlue, the group created a worm that could spread from machine to machine, infecting them. "It's stressful enough for someone going through recovery or treatment for cancer".

"[The] worldwide ransomware attack shows what can happen when the NSA or Central Intelligence Agency write malware instead of disclosing the vulnerability to the software manufacturer", Lieu said in a statement.

"It's an global attack and a number of countries and organizations have been affected", she said.

As companies and individuals take stock Monday morning, the focus is turning to protecting against further attacks. Authorities said they were communicating with more than 100 energy, transportation, telecommunications and financial services providers about the attack.

In Spain, some big firms took pre-emptive steps to thwart ransomware attacks following a warning from Spain's National Cryptology Centre of "a massive ransomware attack". Lieu said it is "deeply disturbing" the NSA likely wrote the original malware used to ransom computers.

The cyberattack that spread malicious software around the world, shutting down networks at hospitals, banks and government agencies, was thwarted by a young British researcher and an cheap domain registration, with help from another 20-something security engineer in the U.S.

He said many NHS hospitals in Britain use Windows XP software, introduced in 2001, and as government funding for the health service has been squeezed, "IT budgets are often one of the first ones to be reduced".