Ransomware is the top data breach threat facing health-care organizations, highlighting the need for better employee training, according to research from Bloomberg Law.

Ransomware attacks were the leading cause of 68 of 602 health-care data breaches reported to the government between 2016 and 2018 and resolved by March 2019, a Bloomberg Law analysis found. Mailing errors were second, accounting for 52 of the data breaches.

The attacks often piggyback on email attachments, and a lack of training can lead employees...