Let me tell you that this site is very informative about Social Security information - www.Social-Security.biz.
It starts out when you apply with this Form SS-5 to get a Social Security Number.
Purpose of the Form References are to the IRS code unless otherwise noted. A person who is required to file an information return with the IRS must obtain your correct taxpayer identification number (TIN) to report, for example, income paid to you, real estate transactions, mortgage interest you paid, acquisition or abandonment of secured property, cancellation of debt, or contributions you made to an IRA. Use Form W-9 only if you are a U.S. person (including a resident alien), to provide your correct TIN to the person requesting it (the requester) and, when applicable, to:
1. Certify that the TIN you are giving is correct, (or you are waiting for a number to be issued)
2. Certify that you are not subject to backup withholding, or
3. Claim exemption from backup withholding if you are a U.S. exempt payee. If applicable, you are also certifying that as a U.S. person, your allocable share of any partnership income from a U.S. trade or business is not subject to the withholding tax on foreign partners share of effectively connected income.
Note. If a requester gives you a form other than Form W-9 to request your TIN, you must use the requester’s form if it is substantially similar to this Form W-9. Definition of a U.S. person. For federal tax purposes, you are considered a U.S. person if you are: An individual who is a U.S. citizen or U.S. resident alien, A partnership, corporation, company, or association created or organized in the United States or under the laws of the United States, An estate (other than a foreign estate), or A domestic trust (as defined in Regulations section 301.7701-7).
Download and read the form SS-5 to get all of the information on it.
There is more to read if you are interested.