A massive ransomware attack appears to have hit many organizations around the world, including Britain's health-care system, Russia's Interior Ministry, and Spanish firms.
Computers have reportedly been locked in thousands of locations around the world by a program, known as WannaCry, that demands $300 ransom in Bitcoin.
Reports say some 50,000 attacks affected as many as 74 countries, including Britain, the United States, China, Russia, Spain, Italy, and Taiwan.
The BBC reports that experts have linked the attacks to vulnerabilities released by a group known as The Shadow Brokers. The group has recently claimed to have dumped hacking tools stolen from the U.S. National Security Agency (NSA).
Irina Volk, a spokeswoman for Russia's Interior Ministry, told TASS news agency, that only some 1,000 computers -- or less than 1 percent of the ministry's computers -- were infected, "thanks to the timely measures" taken by the ministry. Volk said the ministry's servers were not infected.
At least 16 National Health Service (NHS) organizations in Britain were hit by the ransomware attacks.
"A number of NHS organizations have reported to NHS Digital that they have been affected by a ransomware attack," NHS Digital, the health service's IT division, said in a statement.
The attack was not specifically targeted at the NHS and was "affecting organizations from across a range of sectors," the statement said.
"At this stage we do not have any evidence that patient data has been accessed," it said.
Several hospitals in London and other parts of England were affected, with IT systems reportedly turned off, causing delays at some hospitals.
The cyberattack on the NHS was part of a wider "international attack," Prime Minister Theresa May said.
A number of Spanish firms were also among the victims. Telecoms giant Telefonica said in a statement that it was aware of a "cybersecurity incident" but that clients and services had not been affected.
Power firm Iberdrola and utility provider Gas Natural were also reported to have been affected by the attack.
Reports of attacks also came from Italy and Portugal, where the local Telecom company confirmed the attack. Delivery company FedEx also confirmed the attack, although it did not clarify in which territories it had been hit.
Jakub Kroustek of the Avast cybersecurity software company, based in the Czech Republic, said he had logged tens of thousands of attacks worldwide.
"According to our data, the ransomware is mainly being targeted to Russia, Ukraine, and Taiwan, but the ransomware has successfully infected major institutions, like hospitals across England and Spanish telecommunications company Telefonica," Kroustek wrote in a blog post on the Avast website.
With reporting by Reuters, AP, AFP, dpa, and BBC