2013 Nielsen — HR spreadsheet accidentally emailed internally with employee SSNs
Data compromised
Names and U.S. SSNs for an undisclosed employee cohort
Technical writeup
Nielsen Audio acknowledged that a human-resources staffer mass-mailed a spreadsheet with employee names and Social Security numbers to colleagues in December 2013, constituting an internal misdelivery rather than an external intrusion. SC Media and follow-on trade coverage described containment via mailbox purges and substitute notifications.
Root cause
Misdirected bulk email attachment (human error)