Social security numbers are assigned using a randomization process that was put into effect on June 25, 2011, according to the Social Security Administration. This process assists in protecting the overall integrity and the longevity of the number through the years.
Prior to the change in June of 2011, the Social Security Administration comprised the numbers through a very strategic process. The first three numbers of the nine-digit number were based on the zip code provided on the card application. The second two numbers reflected the group number. These were followed by a four-digit serial number customized for each card holder. According to the Social Security Administration, any number beginning with 000 will never be a valid social security number.
Initially, Social Security numbers were implemented for the sole purpose of tracking a worker's earnings history to better calculate benefit entitlement and levels after working age. Today, social security numbers are used for more substantial purposes, such as to gather information about an individual prior to lending money or offering a job.
The Social Security Administration began assigning numbers and preparing cards through United States Postal Service offices, as there were no field offices in operation to handle the preparation of the cards prior to October 14, 1936.