This post is from GRS staff writer April Dykman.

In articles about how to prevent identity theft, I’ve often read that one should never give out his or her social security number (SSN) unless absolutely necessary. That sounds like good common sense. But I recently found myself asking, in what situations is it actually necessary?

I’ve mentioned that my husband and I own land on which we are starting to build a home. The land is owner-financed, and we’ve had a great relationship with the sellers (who are also our future neighbors) for the past three years. Last week I received a message that they needed our SSNs. The full story wasn’t clear, but it seemed they had a new CPA who said she needed our numbers to complete their taxes. This immediately set off red flags for me. This isn’t to say I distrust the sellers. They are a lovely retired couple — the kind of people that invite you in for coffee when you drop off the monthly payment. But I didn’t know this CPA, why she needed our SSNs when they’ve never been needed before, and what precautions she would take to safeguard them. So I decided to dig a little deeper. Do you have to provide your SSN because it’s requested, and if not, how do you know which situations are optional?

Social security numbers: Why they matter
Someone illegally using your number can access personal information and apply for and use credit in your name, creating a financial mess that you’re left to sort out. Creditors can start calling, and you might be turned down for loans.

According to the 2010 Identity Fraud Survey Report, last year more than 11 million people in the U.S. were victims of identity fraud — at a total cost of $54 billion. The good news is that most victims didn’t have any out-of-pocket requests, and those who did paid an average of $373. But the average time the victims had to spend to resolve the situation was 21 hours. Yuck.

It’s important that you safeguard your number, taking the following precautions:

  • Keep your social security card in a secure place, which does not include keeping it in your wallet.
  • Consider your number confidential. When writing a check, firmly deny requests to write your SSN on the check. If an entity uses your SSN as your account number, request that it be changed.
  • Don’t respond to e-mail requests for your SSN, even if they seem to be from a legitimate company with which you do business. Same goes for unsolicited phone calls.
  • If an online company requires your SSN, such as for an insurance quote, make sure the server is secure and the company is reputable.
  • Request your free credit reports each year to ensure no unusual credit lines appear.

When your SSN is required
In certain situations, you’ll have to provide your SSN, such as the following:

  • When you start a new job, your employer will request your number. Your name and number must be accurate in your employer’s payroll records and W-2 so that Social Security can credit your earnings.
  • Your financial institutions need your number for tax reporting purposes.
  • Some government agencies, such as motor vehicle departments, can require your number. All agencies, from local to federal, must disclose whether your SSN is required or optional, how it will be used, and under what authority it’s being requested.

When it’s requested, but not required
Any business can request your SSN, and there aren’t many restrictions on what the business can do with it. Information resellers, consumer reporting agencies, and some health care organizations obtain SSNs and use them in a variety of ways. But when it’s not required by law, you can refuse to provide it (the flip side is that the business also can refuse to do business with you). If a business requests your number, ask the following questions:

  • Why is my SSN needed?
  • How will it be used?
  • Is it required by law (if so, state the law or regulation)?
  • What security measures does your company take with customer SSNs?
  • What happens if I refuse to provide it?

You also can ask to speak with a manager or supervisor to explain your concern about identity theft, and ask that they accept another identifier in place of your SSN. If you still can’t persuade them and don’t feel comfortable giving out your number, be willing to walk away and find another company with which to do business.

In our case, the sellers said they no longer needed our SSNs because it was only required if they filed their taxes online, and they decided not to do so. I don’t suspect anything fraudulent in our situation, but even so, it’s prudent to keep your SSN confidential, even if you have to be a pain in the neck about it. A request for your SSN doesn’t mean it’s a requirement.