They want your social security number at the doctor’s office, at the bank — heck, they want it when your teen signs up to take the SAT. But do you have to provide it? And how safe is it to do so? 

With massive data breaches becoming common and increasing awareness of identity theft, it's clear just how vital it is to keep important personal data, especially our Social Security numbers, private. That number — originally designed to keep track of Social Security benefits but also used for income taxes and a variety of benefit programs — can be the key to a thief obtaining credit in your name and unleashing a problem that some consumers spend years trying to correct.

Who can ask for it?

Just about anyone can ask for you SSN, but not everyone has the legal right to do so.

Many government agencies, including taxing authorities and departments of motor vehicles, do, according to the Privacy Rights Clearinghouse, a national authority on the subject. All government agencies, regardless of what level, are required to provide a statement on any form that asks for that number explaining whether the request is mandatory or optional.

You'll also be on the hook to provide your SSN when you're doing business with a company that has to report its dealings with you for tax purposes, including an employer or a financial institution. In addition, applications for credit typically require use of your number because it allows a search of credit records in a way that should avoid confusion between you and anyone else with a similar name.

For the most part, according to Privacy Rights Clearinghouse, you are not obligated to provide your SSN to most businesses and health care providers. Of course, if you refuse to provide it, they can refuse you service.

"If a business insists on knowing your SSN when you do not see a reason for it, we encourage you to speak to a manager who may be authorized to make an exception or who may know whether company policy requires it," advises the Privacy Rights Clearinghouse on their website.

Protecting your SSN

When you're online and you are asked for your Social Security number, think before entering it into a form for such things as a credit card application. Be sure you are dealing with a legitimate company and that you are on a secure site. (Secure sites will have a web address that begins with https instead of http.)

Never send your number in response to an email. Such requests, even when they appear legitimate, are typical of a type of scam called "phishing." Getting that number is often the last piece of information a crook needs in order to steal your identity.

More practices to avoid:

  • Never list an SSN when posting a paper record on a public bulletin board
  • Never send SSNs via an electronic format, like instant messaging or email
  • Never use a computer log-in system where you have to use your SSN, unless it's a website that begins with https
  • Never use SSNs on ID cards (if you have a choice)
  • Never send SSNs on postcards
  • Never store SSNs on unprotected computer systems
  • Never carry a Social Security card with you unless need it that one day (like when you start a new job)

Refusing to give your number

If you are not obligated to provide the number and you want to hold off, simply omit the information or write "refused" or “N/A," the Privacy Rights Clearinghouse suggests.

Explain why you don't want to use that number and ask for someone to explain why it is necessary. Suggest the possibility of using a different piece of identification, such as a driver's license number.

What about providing just the last four digits?

Being asked for the last four digits of your Social Security number is really only of value to a company that already has it. Typically, that would be a utility or financial services company that uses those numbers in attempt to verify you are who you say you are. Giving out just those digits would serve no other purpose.

Mitch Lipka is a consumer columnist and product safety expert. He was the 2011 recipient of the "Kids Best Friend Award" from Kids In Danger for his commitment to reporting on children’s product safety.