September 2015 — XcodeGhost malware, 128M iPhones via infected App Store apps
Data compromised
Device identifiers, app data
Technical writeup
Malicious Xcode used by developers in China; 4k+ apps on App Store; 128M users (18M US). Apple did not disclose to users; extent revealed in Epic lawsuit 2021.
Root cause
Compromised toolchain; malicious apps.