In early 2016, Apple discovered what it believed was a potential security vulnerability in at least one data center server it purchased from a U.S.-based manufacturer, Super Micro Computer, according to a Super Micro executive and two people who were briefed about the incident at Apple. The server was part of Apple’s technical infrastructure, which powers its web-based services and holds customer data.

Apple ended up terminating its yearslong business relationship with Super Micro, according to Tau Leng, a senior vice president of technology for Super Micro, and a person who was told about the incident by a senior infrastructure engineering executive at Apple. The tech giant even returned some of Super Micro’s servers to the company, according to one of the people briefed about the incident.