EY data breach hits Big Four security

What happened: EY said an unauthorised third party accessed a platform used by its IT teams and downloaded client documents, potentially exposing sensitive tax services information. The hack was linked to a vulnerability in Checkmarx software. Key numbers: Access occurred between March 28 and April 12, 2026. Why it matters: Senior technology partners at Big Four firms said interconnected global networks and client communication channels create risks. A Gartner analyst said a consistent, measurable security baseline across member firms and critical providers is the practical priority.

EY said an unauthorised third party accessed a platform used by its IT teams and downloaded client documents, potentially exposing sensitive tax services information. The hack was linked to a vulnerability in Checkmarx software.

Senior technology partners at Big Four firms said interconnected global networks and client communication channels create risks. A Gartner analyst said a consistent, measurable security baseline across member firms and critical providers is the practical priority.