Paris, France — A new, highly virulent strain of malicious software that is crippling computers globally appears to have been sown in Ukraine, where it badly hobbled much of the government and private sector on the eve of a holiday celebrating a post-Soviet constitution.

The fresh cyber-assault Tuesday leveraged the same intrusion tool as a similar attack in May and proved again just how disruptive to daily life sophisticated cyber-assaults can be in this age of heavy reliance on computers.

Hospitals, government offices and major multinationals were among the casualties of the ransomware payload, which locks up computer files with all-but-unbreakable encryption and then demands a ransom for its release.

Ukraine and Russia appeared hardest hit. In the United States, it affected companies such as the drugmaker Merck and Mondelez International, the conglomerate of food brands such as Oreo and Nabisco.

Multinationals, including the global law firm DLA Piper and Danish shipping giant A.P. Moller-Maersk, were also affected.

The virus' pace appeared to slow by Wednesday, 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.