Merck, a U.S.-based pharmaceutical giant, was among dozens of businesses affected by a sprawling cyberattack Tuesday, with victims worldwide facing demands to pay a ransom or have their computer networks remain locked and inaccessible.

The widespread intrusion that hit the New Jersey-based drug company was similar to the major ransomware attack last month, which deployed a virus dubbed WannaCry. Merck also has a European presence, with an office in Ukraine, where many of the ransomware attacks were concentrated.

The extent of the Merck hack is not yet known.

Merck employees arrived at their offices Tuesday morning to find a ransomware note on their computers. The company confirmed via Twitter soon after that its "network was part of a global hack."

Employees were told to get off their computers and go home, said one scientist who works at a Merck lab in New England. "Some people looked like they had their hardware wiped - it just shut down the whole network site," said the employee, who spoke on the condition of anonymity because she was not authorized to discuss the matter.

All U.S. offices of Merck were affected, she said. "Without computers these days, you can't do anything," she added. As a scientist, her instruments are connected to a computer, her data is stored on central servers, and the safety data sheets are all online. "It's one thing to have our laptop be corrupted. We're really hoping that all the data [in the central servers] is protected. But we don't know that."

She said employees at her office were informed over a public address system, and people spread the word to colleagues by cellphone. Employees were told to call a number used for snow emergencies to find out whether they should report to work Wednesday.

Merck officials didn't immediately respond to a request for comment.

Tuesday's attack used a virus similar to one known as Petrwrap or Petya, security researchers said, and exploited a vulnerability that the National Security Agency discovered years ago.

"The emergence of Petya and WannaCry really points out the need for a response plan and a policy on what companies are going to do about ransomware," said Mark Graff, the chief executive of Telagraff, a cybersecurity company. "You won't want to make that decision at a time of panic, in a cloud of emotion," he said.

DLA Piper, a multinational law firm with an office in Washington, D.C., also was hit by the ransomware, according to a statement on its website.