A Social Security number (SSN) is a nine-digit number issued by the Social Security Administration to all U.S. citizens, as well as non-citizens who have permission from Homeland Security to work in the United States. A SSN is necessary to report wages, collect Social Security benefits and qualify for other government programs.
For SSNs assigned before 1972, the first three numbers reflect the state where you applied for the number. After 1972, the first three digits reflect the zip code in the mailing address on your application for the SSN.
The Social Security Administration has never issued a number in the 800 or 900 range. Therefore, a number beginning in 999 is not valid.
Some universities have assigned nine-digit “temporary” Social Security numbers to post-graduate foreign nationals beginning with 999. The temporary number is designed to be replaced once the graduate student has received a valid SSN.
A number beginning in 999 may be an Individual Taxpayer Identification Number (ITIN), a tax processing number issued by the Internal Revenue Service (IRS). This number is also nine digits, and it always begins with the number nine.
If you’re given a 999 Social Security number, consider it a fraudulent number. The Social Security Administration maintains the Social Security Number Verification Service to help verify fraudulent numbers.