LONDON - Friday's cyber attack hit 200,000 victims in at least 150 countries and that number could grow when people return to work on Monday, the head of the European Union's police agency said on Sunday.

Cyber security experts say the spread of the virus dubbed WannaCry - "ransomware" which locked up computers in car factories, hospitals, shops and schools in several countries - has slowed, but that any respite might be brief.

Europol Director Rob Wainwright told a British television program the attack was unique in that the ransomware was used in combination with "a worm functionality" so the infection spread automatically.

"The global reach is unprecedented. The latest count is over 200,000 victims in at least 150 countries, and those victims, many of those will be businesses, including large corporations," he said.

"At the moment, we are in the face of an escalating threat. The numbers are going up; I am worried about how the numbers will continue to grow when people go to work and turn (on) their machines on Monday morning."

He said Europol and other agencies did not yet know who was behind the attack but "normally it is criminally minded and that is our first working theory for obvious reasons".

"(There have been) remarkably few payments so far that we've noticed as we are tracking this, so most people are not paying this, so there isn't a lot of money being made by criminal organizations so far," he said.

As terrifying as the attack was, cybersecurity experts say it's nothing compared to what might be coming especially if companies, organizations and governments don't make major fixes.

Had it not been for a young cybersecurity researcher's accidental discovery of a so-called "kill switch," the malicious software likely would have spread much farther and faster. Security experts say this attack should wake up every corporate board room and legislative chamber around the globe.

Darien Huss, a 28-year-old research engineer who assisted the anonymous British researcher who stopped the virus from spreading, said he was "still worried for what's to come in the next few days because it really would not be so difficult for the actors behind this to rerelease their code without a kill switch or with a better kill switch. Or we could potentially see copycats mimic the delivery or exploit method they used."

Reuters - AP