This is great information to keep in mind.

We carry around far too much identifying information. You shouldn't be toting your passport, birth certificate, and the credit cards you're not using. (In fact, if you haven't used them in some time, close the accounts.) Most importantly, don't carry around your Social Security card. Why? Your Social Security number is key for an identity thief because it can be used to apply for credit or other loans in your name. There are only a few valid occasions to give it out.

• When you're applying for a job
  
• When you're doing your taxes
  
• When you're involved in a stock or other financial transaction

In most other cases, the person asking for the number wants to use it for identification purposes. Ask if they'll substitute for another number instead. Even states that use Social Security numbers as driver's license numbers are often willing to make a switch.