"A genie let out of a bottle of this kind, especially created by secret services, can then cause damage to its authors and creators", Putin said.
Russian President Vladimir Putin denied that his country, which has been accused of cyber meddling in several countries in recent years, had anything to do with the attack.
The Japan Computer Emergency Response Team Coordination Center, a nonprofit group, said 2,000 computers at 600 locations in Japan were affected.
Microsoft blamed the US government for "stockpiling" software code that was used by unknown hackers to launch the attacks.
"There are other criminals who've launched this attack, and they are ultimately responsible for this", he said.
"An equivalent scenario with conventional weapons would be the United States military having some of its Tomahawk missiles stolen", Smith wrote. It was presumably placed there just in case the hackers wanted to make it stop.
The cross-border police agency Europol said the situation was now "stable", defusing concerns that attacks that struck computers in British hospital wards, European auto factories and Russian banks would spread further at the start of the working week. So far, not many people have paid the ransom demanded by the malware, Europol spokesman Jan Op Gen Oorth told The Associated Press.
Always update systems and software with the latest security updates.
The ransomware exploits older versions of Microsoft's operating system software, such as Windows XP. But computers and networks that haven't updated their systems are at risk.
Based on initial reports, only one Australian business was hit by the cyber attack.
French carmaker Renault said its Douai plant, one of its biggest sites in France employing 5,500 people, would be shut on Monday as systems were upgraded.
"We've never seen anything like this", the head of the European Union's policing agency told Britain's ITV television, calling its reach "unprecedented".
Tehran mayor Qalibaf quits presidential race, backs Raisi: ISNA
Raisi has been campaigning on that, proposing cash payments for the poor that proved popular in the past under Ahmadinejad. Rouhani added that tourism in 2013, before the deal lifted some sanctions, was less than that recorded in April this year.
"I highly suspect that, with the amount of coverage that this incident is getting, there are probably already people that are working to incorporate the exploit that was used for spreading", he said.
It encrypted users' computer files and displayed a message demanding anywhere from $300 to $600 to release them; failure to pay would leave the data mangled and likely beyond fix.
The perpetrators have demanded payment within three days or the price will double, and they threaten to delete the files altogether if payment is not received within seven days.
Victims were asked for payment of $300 (275 euros) in the virtual currency Bitcoin. They are doing the same with the "phishing" emails that helped the ransomware embed itself in computers.
The hackers use the tool to encrypt files within targeted computers, "locking" the files and making them inaccessible.
"The recent attack is at an unprecedented level and will require a complex worldwide investigation to identify the culprits", said Europol, Europe's policing agency.
The British government denied allegations that lax cybersecurity in the financially stretched, state-funded health service had helped the attack spread.
Symantec said the majority of organisations affected were in Europe.
Russia's interior ministry said some of its computers had been hit, while the country's banking system was also attacked, although no problems were detected, as was the railway system.
"We will ensure that we re-schedule any cancelled appointments as soon as possible".
Hospitals, universities, manufacturers and government agencies in the U.K., China, Russia, Germany and Spain have all been affected.