More than 200,000 computers in at least 150 countries have so far been infected, according to Europol, the European Union's law enforcement agency, Bloomberg reported.
The U.K.'s National Cyber Security Centre said new cases of so-called ransomware are possible "at a significant scale."
"We've seen the rise of ransomware becoming the principal threat, I think, but this is something we haven't seen before -- the global reach is unprecedented," Europol Executive Director Rob Wainwright said on ITV's "Peston on Sunday" broadcast.
Read alsoBBC: Ransomware infections reported worldwideThe malware used a technique purportedly stolen from the U.S. National Security Agency. It affected the U.K.'s National Health Service, Russia's Ministry of Interior, Germany's Deutsche Bahn rail system, automakers Nissan Motor Co. and Renault SA, PetroChina, logistics giant FedEx Corp., and other company and hospital computer systems in countries from Eastern Europe to the U.S. and Asia.
The hackers used the tool to encrypt files within affected computers, making them inaccessible, and demanded ransom -- typically $300 in bitcoin. Russia and Ukraine had a heavy concentration of infections, according to Dutch security company Avast Software BV.
Microsoft Corp. President Brad Smith, in a blog post Sunday, said the attack is a "wake-up call" for governments in the U.S. and elsewhere to stop stockpiling tools to exploit digital vulnerabilities. "They need to take a different approach and adhere in cyberspace to the same rules applied to weapons in the physical world," he said.
