Social Security Number of all time was 078-05-1120. In 1938, a wallet manufacturer decided to promote its product by showing how a Social Security card would fit into its wallets. A sample card, used for display purposes, was inserted in each wallet. The company vice president thought it would be a clever idea to use the actual SSN of his secretary, Mrs. Hilda Schrader Whitcher.
Even though the card was only half the size of a real card and had the word 'specimen' written across the face, many purchasers of the wallet adopted the SSN as their own. In the peak year of 1943, 5,755 people were using Hilda's number. As late as 1977, 12 people were found to still be using the SSN.
(via Bits & Pieces)