The cross-border police agency Europol said the situation was now "stable", defusing concerns that attacks that struck computers in British hospital wards, European vehicle factories and Russian banks would spread further at the start of the working week.
The indiscriminate attack was unleashed Friday, striking hundreds of thousands of computers worldwide by exploiting known vulnerabilities in older Microsoft computer operating systems.
But he also blamed the governments. The hackers exploited software code from the National Security Agency that leaked online.
"An equivalent scenario with conventional weapons would be the US military having some of its Tomahawk missiles stolen", attorney Brad Smith wrote on Microsoft's blog.
"It is important to understand that the way these attacks work means that compromises of machines and networks that have already occurred may not yet have been detected, and that existing infections from the malware can spread within networks", the NSCC said in a statement. The virus took control of users' files, demanding payments to restore access.
Ryan Kalember, senior vice president at Proofpoint Inc., says that millions of devices could be vulnerable if they haven't applied security patches over the weekend. "We haven't fully dodged this bullet at all until we're patched against the vulnerability itself". It encrypted users' computer files and displayed a message demanding $300 to $600 worth of the digital currency bitcoin to release them; failure to pay would leave the data scrambled and likely beyond fix.
Some security experts expect a second wave of the attack to start Monday morning, as employees arrive at work and turn on affected computers.
"More action is needed, and it's needed now", he said.
In an interview with Britain's ITV, Europol Director Rob Wainwright said a cross-border investigation would be necessary to track down the culprits. Europol that said the malware has claimed some 200,000 victims across 150 countries and that the numbers are still going up.
NHS hospitals are still struggling in the fight against a global ransomware attack, with computer systems in several hospitals locked three days after the initial outbreak and previously unaffected hospitals revealed to have fallen to WannaCrypt ransomware.
President Vladimir Putin denied Russian Federation, which has been accused of cyber meddling in several countries around the world in recent years, had anything to do with an attack that hit hundreds of thousands of computers. "The bad guys are always one step ahead".
Major global companies said they also came under attack. The official was not authorized to discuss the private meetings by name and requested anonymity.
He said it was too early to say who is behind the onslaught and what their motivation was.
"Right now, just about every IT department has been working all weekend rolling this out", Dan Wire, spokesman at Fireeye Security, said. But, because of the widespread and massive exploit across the world, Microsoft has issued a free-to-all Windows XP patch to help protect computers.
"In particular, making sure that our data is properly backed up and making sure that we are using the software patches, the anti-virus patches, that are sent out regularly by manufacturers".
Disable your computer's Server Message Block service.
Microsoft distributed the patch two months ago, which could have forestalled much of the attack, but in many organizations it was likely lost among the blizzard of updates and patches that large corporations and governments strain to manage.
Smith also wrote that "cybersecurity has become a shared responsibility between tech companies and customers".