Here are some of the most prominent victims, from Britain's National Health Service (NHS) to French carmaker Renault and the Russian interior ministry.
NHS
The British public health service - the world's fifth-largest employer, with 1.7 million staff -- was badly hit, with interior minister Amber Rudd saying around 45 facilities were affected. Several were forced to cancel or delay treatment for patients.
Pictures on social media showed screens of NHS computers with images demanding payment of $300 (230 pounds, 275 euros) in the virtual currency Bitcoin, saying: "Ooops, your files have been encrypted!"
Renault
The French automobile giant was hit, forcing it to halt production at sites in France and its factories in Slovenia and Romania as part of measures to stop the spread of the virus.
Nissan UK's unit in Sunderland was hit by the attack, spokeswoman Lucy Banwell said.
Russian banks and ministries
Russia's central bank was targeted, along with several government ministries and the railway system. The interior ministry said 1,000 of its computers were hit by a virus. Officials played down the incident, saying the attacks had been contained.
Germany railways
Germany's Deutsche Bahn national railway operator was affected, with information screens and ticket machines hit. Travellers tweeted pictures of hijacked departure boards showing the ransom demand instead of train times. But the company insisted that trains were running as normal.
Fedex
The US package delivery group acknowledged it had been hit by malware and said it was "implementing remediation steps as quickly as possible."
Telefonica
The Spanish telephone giant said it was attacked but "the infected equipment is under control and being reinstalled," said Chema Alonso, the head of the company's cyber security unit and a former hacker.
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