Q: "Is it illegal to have multiple social security numbers? What about multiple aliases? Sometimes people have slight variations on their names with entirely different social security numbers. Isn't this illegal? What are the possible repercussions?"
A: The quick answer to your question is "Yes, it is generally illegal to have multiple social security numbers."
According to the Social Security Act, a person commits SSN misuse when they: “…willfully, knowingly, and with intent to deceive the Commissioner of Social Security as to his true identity (or the true identity of any other person) furnishes or causes to be furnished false information to the Commissioner of Social Security.…”
You are required to provide the SSA with any aliases when you apply for a social security number. The only way you could be given multiple SSNs is if you failed to supply that information and provided documentation that established your alternate identity. That's illegal.
One can use multiple aliases for informal purposes. But the SSA generally issues only one SSN per proper person, so you can't legally use aliases to establish alternate identities with the SSA. The use of an alternate identity to establish eligibility for and to receive multiple benefits under various government programs is fraud.
Violation of federal law may be investigated by any number of federal agencies-- the most well known the Federal Bureau of Investigation (FBI)-- and result in federal prosecution. If found guilty you might have to pay restitution, pay a fine, or be incarcerated in a federal prison.
[This is not legal advice. You should consult a licensed attorney-at-law for legal advice or representation before making decisions that may affect your legal rights.]