Cyber attack
Cyber attackIstock

The massive ransomware cyber-attack which affected computers across eastern Europe yesterday has spread to the US, with a large pharmaceutical company acknowledging that it has been affected by the malware.

New Jersey-based Pharmaceutical giant Merck stated Tuesday that it had been unable initially to contain the damage caused by the virus to its computers, which use Windows operating systems.

“We confirm our company’s computer network was compromised today as part of global hack,” Merck stated on its Twitter account. “Other organizations have also been affected.”

“We are investigating the matter and will provide additional information as we learn more," the company added.

A massive cyber-attack struck several European countries yesterday, including Ukraine, Russia and Denmark.

The ransomware attack locked out computers and the users received demands to pay the criminal hackers to have them unlocked.

The Central Bank of Ukraine confirmed that an "unknown virus" is behind the attack, but did not specify which banks have been affected.

The sensors at the Chernobyl nuclear power plant were shut down as well, forcing staff to monitor radiation levels manually.

"This is an unprecedented attack, but our most important systems have not been affected," said Ukrainian Prime Minister Volodymyr Groisman.

"The current cyber attack is the largest in the history of Ukraine and we believe that the source is Russia, even though it has reported a number of attacks on its own," the Interior Ministry said.

Merck has offices in Kiev, the capital of Ukraine.