2010 — Citigroup: About 600,000 Citigroup customers got a shock…
Data compromised
Personal information
Technical writeup
About 600,000 Citigroup customers got a shock earlier this month when
they received their annual tax documents with their Social Security
numbers printed on the outside of the envelope. The digits were not
identified as a Social Security number, and they were printed at the
lower edge of the mailing envelope with other numbers and letters that
together resembled a mail routing number.
Root cause
Unintended disclosure