Dental practices throughout the United States were the victims of a ransomware attack this week, according to ZDNet—a business technology news site. A source reported to ZDNet that hundreds of practices were the targets of a ransomware gang that compromised a software provider and used its product to deploy ransomware on customers’ systems.

The targeted practices were using DDS Safe, a medical records retention and backup software from two Wisconsin-based companies—The Digital Dental Record and PerCSoft.

According to ZDNet, a hacker group breached the infrastructure behind the software and used it to deploy the REvil (Sodinokibi) ransomware on the affected computers.

The breach was detected Monday, August 26, 2019, when the affected practices could not longer access patient records.

According to ZDNet’s source, The Digital Dental Record and PerCSoft paid the ransom demand and received the key recover practice files. ZDNet also reports that this is the third time a hacker group has compromised a managed service provider and used its infrastructure to deploy the REvil ransomware.

The REvil ransomware has been ranked as one of the most active and widespread ransomware strains this year, with a 12.5% marketshare.