Researchers say the latest cyberattack is linked to ransomware which hit the world last month. Russia and Ukraine were the worst affected while operations at major companies were also disrupted in Europe and India.
A major global cyberattack disrupted computers at Russia's biggest oil company, Ukrainian banks and multinational firms with a virus similar to the ransomware that infected more than 300,000 computers last month .
The rapidly spreading cyberextortion campaign, which began on Tuesday, also reportedly hit businesses in the Asia-Pacific region on Wednesday.
Operations of several European companies were hit, including India's largest container port, although the impact on companies and governments across the wider region appeared to be limited.
The ransomware virus includes code known as Eternal Blue, which cybersecurity experts widely believe was stolen from the US National Security Agency (NSA) and was also used in last month's ransomware attack, named WannaCry.
"Cyber attacks can simply destroy us," said Kevin Johnson, chief executive of cybersecurity firm Secure Ideas.
"Companies are just not doing what they are supposed to do to fix the problem."
The virus crippled computers running Microsoft Corp's Windows by encrypting hard drives and overwriting files, then demanded $300 in bitcoin payments to restore access.
More than 30 victims paid into the bitcoin account associated with the attack, according to a public ledger of transactions listed on blockchain.info.
Microsoft said the virus could spread through a flaw that was patched in a security update in March.
"We are continuing to investigate and will take appropriate action to protect customers," a spokesman for the company said, adding that Microsoft antivirus software detects and removes it.
TRT World's Sara Firth reports from London.
Russia, Ukraine worst hit
The first attacks were reported from Russia and Ukraine which, according to Kaspersky Lab, were most affected by the thousands of attacks.
Other victims spread across countries including Britain, France, Germany, Italy, Poland and the United States.
The total number of attacks was unknown.
Russia's Rosneft, one of the world's biggest crude producers by volume, said its systems had suffered "serious consequences" but said oil production had not been affected because it switched over to backup systems.
Ukrainian Deputy Prime Minister Pavlo Rozenko said the government's computer network went down and the central bank reported disruption to operations at banks and firms, including the state power distributor.
WPP, the world's largest advertising agency, said it was also infected. A WPP employee who asked not to be identified said workers were told to shut down their computers. "The building has come to a standstill," the employee said.
A Ukrainian media company said its computers were blocked and had received the ransom demand.
Russia's central bank said there were isolated cases of lenders' IT systems being infected. One consumer lender, Home Credit, had to suspend client operations.
Operations at one of the three terminals of Jawaharlal Nehru Port (JNPT) in Mumbai, India's largest container port, were disrupted.
The impacted terminal is operated by Danish shipping giant AP Moller-Maersk, which also reported disruptions in Los Angeles.
JNPT chairman Anil Diggikar said the port has been trying to clear containers manually and is operating at about a third of its capacity.
India-based employees at Beiersdorf, makers of Nivea skincare products, and Reckitt Benckiser, which owns Enfamil and Lysol, said the ransomware attack had affected some of their systems.
A Cadbury chocolate factory was hit, a trade union official said.
Production at the Hobart factory on the island state of Tasmania ground to a halt late on Tuesday after computer systems went down.
Cadbury owner Mondelez International said in a statement that overnight staff in various regions were experiencing technical problems but it was unclear whether this was due to a cyber attack.
Cybersecurity firms Kaspersky Lab and FireEye said they had detected attacks in other Asia-Pacific countries but did not provide details.
Smaller than WannaCry
Security experts said they expected the impact to be smaller than WannaCry because many computers had been patched with Windows updates in the wake of the WannaCry ransom attack last month to protect them against attacks using the Eternal Blue code.
Still, the attack could be more dangerous than traditional strains of ransomware because it makes computers unresponsive and unable to reboot, Juniper Networks said in a blog post analysing the attack.
Other security experts said they did not believe that the ransomware released on Tuesday had a "kill switch", meaning that it might be harder to stop than WannaCry was last month.
Researchers said the attack may have borrowed malware code used in earlier ransomware campaigns known as Petya and GoldenEye.
The US Department of Homeland Security said it was monitoring the attacks and coordinating with other countries.
It advised victims not to pay the extortion, saying that doing so did not guarantee access would be restored.
No response from NSA
The White House National Security Council said in a statement there was currently no risk to public safety. The US was investigating the attack and determined to hold those responsible accountable, it said.
The NSA did not respond to a request for comment.
The spy agency has not said publicly whether it built Eternal Blue and other hacking tools leaked online by an entity known as Shadow Brokers.
Several private security experts have said they believe Shadow Brokers is tied to the Russian government, and that the North Korean government was behind WannaCry.
Both countries' governments deny charges they are involved in hacking.