US banking giant Citi has been forced to apologise to around 600,000 customers after sending them year-end tax statements through the post with social security numbers printed on the outside of the envelopes.
A "processing error" meant that the letters, sent via the US Postal Service in January, had the nine digit numbers printed on the lower edge of envelopes, although they were not identified as social security numbers.
The bank sent letters to all affected customers last month apologising and offering free credit monitoring for 180 days but insists "there is little or no risk to you".