Ransomware is causing big headaches for computer users in several countries.
Among the victims has been Britain's National Health Service. Its computers were hacked, preventing hospitals and doctors from having access to data.
It even led to the closure of some clinics.
The U.S. courier giant FedEx and the Spanish telecommunications company Telefonica had their systems hacked, too.
The ransomware, which has been installed into computer systems, demands $300 in bitcoins to restore access.
The cybersecurity-software firm Avast has detected the WanaCrypt0r 2.0 (aka WCry) ransomware in 99 countries. The hardest hit have been Russia, Ukraine, and Taiwan.
"The ransomware changes the affected file extension names to '.WNCRY', so an infected file will look something like: original_name_of_file.jpg.WNCRY, for example," Avast stated on its website. "The encrypted files are also marked by the 'WANACRY!' string at the beginning of the file."
It's suspected to be linked to a program created by the U.S. National Security Agency.
"WanaCrypt0r 2.0 is most likely spreading on so many computers by using an exploit the Equation Group, which is a group that is widely suspected of being tied to the NSA, used for its dirty business," Avast opined. "A hacker group called ShadowBrokers has stolen Equation Group’s hacking tools and has publicly released them. As confirmed by security researcher, Kafeine, the exploit, known as ETERNALBLUE or MS17-010, was probably used by the cybercriminals behind WanaCrypt0r and is a Windows SMB (Server Message Block, a network file sharing protocol) vulnerability."
Avast advised all Windows users to update their systems with the latest available patches.