When experts say North Korea is behind an attack, what they often mean is that Pyongyang is suspected of working with or through a group known as Lazarus.
The researchers said it was too early to confirm that Pyongyang was behind the cyberattacks.
Employees monitor possible WannaCry ransomware attacks at the Korea Internet and Security Agency in Seoul on May 17, 2017.
WannaCry, developed in part with hacking techniques that were either stolen or leaked from the U.S. National Security Agency, has infected more than 300,000 computers since Friday, locking up their data and demanding a ransom payment to release it.
Global cybersecurity firms have pointed at North Korea as the mastermind behind the latest cyberattack.
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Trump has also been tempted to think he's the man who can solve the puzzle of Middle East peace that eluded his predecessors. But Netanyahu spokesman David Keyes said the only topic discussed in the 20-minute conversation was Trump's upcoming visit.
With cyber security experts suspecting a North Korean hacker group behind the massive ransomware attack that created havoc in almost 150 countries since the last weekend, Britain's National Crime Agency (NCA) on Tuesday claimed there was no immediate indication of a second surge of such attack.
"We are not aware of payments that have led to any data recovery", White House Homeland Security adviser Tom Bossert said at a daily briefing.
More than 200,000 computers in 150 countries were hit by the ransomware attack, described as the largest ever of its kind, over the weekend. Ransomware encrypts important files, locking people out of their computers unless they pay up to prevent their entire system from being deleted. Failure to pay would leave the data scrambled and probably beyond fix.
He estimated that more than 300,000 computers were taken down around the world. "We should never underestimate it", Choi said.
The worm is likely to have spread through a channel that links computers running Microsoft Windows in a network.
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Beyond policy issues, his shoving of the Montenegrin prime minister and macho handshakes with Macron deepened the scepticism. Trump criticized Germany's trade surplus with the United States on Tuesday, tying the issue to Berlin's military spending.
It also threatened to dump data from banks using the SWIFT worldwide money transfer network and from Russian, Chinese, Iranian or North Korean nuclear and missile programs.
Choi said that if North Korea's culpability is proven, the world should start taking their capabilities seriously and ensure consequences for such actions. He said based on his conversations with North Korean hackers, the reclusive state had been developing and testing ransomware programmes since August. But, now they come to know that some of the codes this WannaCry Software used were similar to the codes used by a company named Lazarus Group, which is of North Korea.
"For now, more research is required into older version of WannaCry", the researchers said.
In China, foreign ministry spokeswoman Hua Chunying said she had no information to share, when asked about the origin of the attack and whether North Korea might be connected.
"We have underestimated North Korea so far, [assuming ] since North Korea is poor, it wouldn't have any technologies".
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Moldovan Prime Minister Pavel Filip, who usually supports the European Union , denied the accusations. Russia's response will be "quite harsh", Russian Deputy Foreign Minister Grigory Karasin said.
Second, North Korean cyber-attacks have typically been far more targeted, often with a political goal in mind.