Prudent or just paranoid

You are smart to closely guard those prized nine digits. But it's sometimes in your best interest, even necessary, to provide the number to reputable companies and people.

Anytime a transaction generates income for you, you'll need to supply the number for tax purposes, so banks and brokerages really do need it. Beyond that, no simple rule exists.

Paul Stephens of the Privacy Rights Clearing house says you should give out the number if a prospective employer, car insurer or credit-card company, for example, is going to use it to check your credit. The number helps ensure that your report is pulled and not that of some deadbeat who shares your name.

But always ask how the number will be used and secured. If you don't like the answer, ask what happens if you don't provide it. Doctors, hospitals and insurers often ask for the number, but they don't need it (Medicare is the exception). And if your local movie store or gym wants it, just say no.

Finally, don't let your employer or any service provider use the number as your ID. As for giving the number to family members, it's true that identity thieves often know their victims. But handling in-laws isn't in Money Magazine's area of expertise.

The prudent conclusion: Ask why the number is needed and if another ID will do the trick. And don't carry the number on you.