https://www.theguardian.com/technology/2017/sep/19/equifax-credit-firm-march-breach-massive-may-hack-customers

Maligned Atlanta-based agency finally goes public on earlier data breach, which happened in March, following reports company only notified payroll customers

Equifax, the credit monitoring agency that lost personal data of 143 million US customers in a massive hack in May, has revealed that it was also the victim of an earlier breach in March.