Most prominent among the victims: The UK's National Health Service. Dozens of hospitals and medical centers had to be closed. Treatment was postponed, ambulances diverted. Appointments couldn't be made because it was too dangerous. Medical workers had no access to important information.
However, some security firms reported that most of the affected computers were in Russia.
It has been reported that the hackers may have used a tool that was a NSA secret before it was leaked to the public earlier this year.