Ransomware attack before holiday leaves companies scrambling

Businesses scrambled Saturday to contain a ransomware attack that has paralyzed their computer networks, a situation complicated in the U.S. by offices lightly staffed at the start of the Fourth of July holiday weekend.

In Sweden, most of the grocery chain Coop's 800 stores were unable to open because their cash registers weren't working, according to SVT, the country's public broadcaster. The Swedish State Railways and a major local pharmacy chain were also affected.

Cybersecurity experts say the REvil gang, a major Russian-speaking ransomware syndicate, appears to be behind the attack that targeted a software supplier called Kaseya, using its network-management package as a conduit to spread the ransomware through cloud-service providers.

Kaseya CEO Fred Voccola said in a statement late Friday night that the company believes it has identified the source of the vulnerability and will “release that patch as quickly as possible to get our customers back up and running.”

John Hammond of the security firm Huntress Labs said he was aware of a number of managed-services providers — companies that host IT infrastructure for multiple customers — being hit by the ransomware, which encrypts networks until the victims pay off attackers. He said thousand of computers were hit.

“It’s reasonable to think this could potentially be impacting thousands of small businesses,” said Hammond, basing his estimate on the service providers reaching out to his company for assistance and comments on Reddit showing how others are responding.

Voccola said fewer than 40 of Kaseya's customers were known to be affected, but the ransomware could still be affecting hundreds more companies that rely on Kaseya's clients that provide broader IT services.

Voccola said the problem is only affecting its...