A "Mistake" A Slight Bit More Unusual Than Normal

Citibank exposes 600,000 customers' Social Security numbers

"Ralph Remakel received a Citibank letter postmarked Feb. 16 that notified him of a recent Citibank error. It turns out he wasn't the only one.
In late January, Citibank mailed year-end tax statements to 600,000 Citi customers via the U.S. Postal Service that included the customers' Social Security numbers ... on the outside of the envelope.
Citi called the mistake a "processing error."