In some cases, chain reactions fed more widespread disruption.

The Swedish Coop grocery store chain had to close hundreds of stores on Saturday because its cash registers are run by Visma Esscom, which manages servers for a number of Swedish businesses and in turn uses Kaseya.

Brett Callow, a ransomware expert at the cybersecurity firm Emsisoft, said he was unaware of any previous ransomware supply-chain attack on this scale.