It appears to exploit a vulnerability in Windows that, according to the Toronto Star, "was supposedly identified by the U.S". Those who have not installed the new patch introduced by Microsoft are badly affected.
Computers booting up to start the workweek might continue the spread of "WannaCry", a ransomware attack where hackers lock down a computer and threaten to delete all its data unless a ransom is paid.
Here are some of the key players in the attack and what may - or may not - be their fault.
Capitalising on spying tools believed to have been developed by the U.S. National Security Agency, the virus dubbed WannaCry has blocked more than 200,000 computers across the globe, demanding a ransom to unlock them.
Shares in firms that provide cyber security services rose with the prospect that companies and governments would have to spend more money on defences.
"We have reached a turning point where it is not sustainable for governments to think they can retain vulnerabilities for very long", said Ari Schwartz, who oversaw technology security issues at the National Security Council during the Obama administration.
The ACLU, meanwhile, urged Congress to pass a law requiring the government to disclose vulnerabilities to companies "in a timely manner", so that they can patch them as soon as possible.
The ransomware - known as WannaCry - exploits a vulnerability in outdated versions of Microsoft Windows, locking down all of a computer's files.
"The government can't do this alone - they're really going to have to reach out and work with Apple, with Microsoft and Google", Martin said.
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Still, it was Microsoft that wrote the exploitable software to begin with.
If you are using an "obsolete" operating system like Windows XP, pay to convert to Windows 10.
Keep security software up to date. He noted, however, the complexity that can be involved in patching a security hole. You'll often be unable to access your computer while the malware is on it. Multiple backups also help.
Owners of these machines may be tempted to pay the ransom, but don't count on getting your files back, said Matthew Hickey, director of security provider Hacker House.
"It's not rocket science", Litan said.
A company official said films were still being screened as scheduled and the company was investigating. Asked what the company is doing to prevent such exploitations, he cited "basic IT security blocking and tackling".
Experts say the attackers might get more than $1 billion from the scam, although as of Saturday, only $33,000 was deposited into several Bitcoin accounts associated with the ransomware.
Latest development on the issue The Indian Computer Emergency Response Team (CERT-In), the central agency coordinating efforts on cyber security issues, has issued a "critical alert" and has advised the installation of relevant "patches" to protect against any data breaches.
Because the attack occurred on Friday, right before people left their offices and went home for the weekend, many computers weren't affected because they simply weren't in use.