PARIS — A new and highly virulent outbreak of data-scrambling software — apparently sown in Ukraine — caused disruption worldwide Tuesday.

Following a similar attack in May, the fresh assault paralyzed some hospitals and government offices in a dramatic demonstration of how easily malicious programs can bring daily life to a halt.

Ukraine and Russia appeared hardest hit by the new strain of ransomware — malicious software that locks up computer files with all-but-unbreakable encryption and then demands a ransom for its release.

In the United States, the malware affected companies such as the drugmaker Merck and Mondelez International, the owner of food brands such as Oreo and Nabisco.

Also hit was Heritage Valley Health System in Beaver County. Spokesman Suzanne Sakson said the health system was using the same emergency procedures it employs during any disaster.

Heritage Valley is a $480 million network that provides care for residents of Allegheny, Beaver, Butler and Lawrence counties, in Pennsylvania; parts of eastern Ohio; and the panhandle of West Virginia.

Its two hospitals have about 500 beds.

The pace of the virus appeared to slow as the day wore on, in part because the malware appeared to require direct contact between computer networks, a factor that may have limited its spread in regions with fewer connections to Ukraine.

The malware’s origins remain unclear. Researchers picking the program apart found evidence its creators had borrowed from leaked National Security Agency code, raising the possibility that the digital havoc had spread using U.S. taxpayer-funded tools.

Multinational companies, including the global law firm DLA Piper and Danish shipping giant A.P. Moller-Maersk were also affected, although the firms didn’t specify the extent of the damage.