More about SSN:

SSN is the widely accepted acronym that stands for Social Security Number. A SSN is a 9-digit, personal identification number issued to U.S. citizens and temporary (working) residents by the United States Social Security Administration.
A social security number is required to apply for a job, receive any government assistance, file taxes, and obtain a mortgage or credit. For all of these reasons, a SSN is also one of the most private pieces of personal information an individual uses, and should be kept private.
Three different types of Social Security cards are issued. The most common type contains the cardholder's name and number. Such cards are issued to U.S. citizens and U.S. permanent residents. There are also two restricted types of Social Security cards:
• One reads "NOT VALID FOR EMPLOYMENT." Such cards cannot be used as proof of work authorization, and are not acceptable as a List C document on the I-9 form.
• The other reads "VALID FOR WORK ONLY WITH DHS AUTHORIZATION." These cards are issued to people who have temporary work authorization in the U.S. They can satisfy the I-9 requirement, if they are accompanied by a work authorization card.
The Social Security number is a nine-digit number in the format "123-45-6789". The number is divided into three parts.
• The Area Number, the first three digits, is assigned by the geographical region. The Area Number represented the office code in which the card was issued. This did not necessarily have to be in the area where the applicant lived, since a person could apply for their card in any Social Security office.
• The middle two digits are the group number. They have no special geographic or data significance but merely serve to break the number into conveniently sized blocks for orderly issuance.
The group numbers range from 01 to 99. However, they are not assigned in consecutive order. For administrative reasons, group numbers are issued in the following order:
1. ODD numbers from 01 through 09
2. EVEN numbers from 10 through 98
3. EVEN numbers from 02 through 08
4. ODD numbers from 11 through 99
As an example, group number 98 will be issued before 11.
• The last four digits are serial numbers. They represent a straight numerical sequence of digits from 0001-9999 within the group.
Currently, a valid SSN cannot have an area number above 772, the highest area number which the Social Security Administration has allocated.
There are also special numbers which will never be allocated:
• Numbers with all zeros in any digit group (000-xx-xxxx, xxx-00-xxxx, xxx-xx-0000).
• Numbers of the form 666-xx-xxxx, probably due to the potential controversy. Though the omission of this area number is not acknowledged by the SSA, it remains unassigned.
• Numbers from 987-65-4320 to 987-65-4329 are reserved for use in advertisements.