NEW YORK (CNN/Money) - I almost got a cell phone the other weekend. But I opted to protect myself against identity theft instead.

After slogging through mind-numbing details on weekend minutes, calling areas and roaming charges, I cradled a few phones, picked my favorite and asked the clerk for an application.

I started scribbling down my information -- until, that is, I came to the line asking for my Social Security number.

They have got to be kidding, I thought. What on earth do they need that for?

To check your credit, a clerk with a wheezy head cold told me. So my name, address, credit card, phone numbers, birth date and cholesterol levels weren't enough, huh? Nope. He couldn't sell me a plan without it. Or rather, he could...if I wanted to put down the equivalent of a year's worth of payments as a deposit.

Gee, thanks.

Before I let loose on the hapless employee, who clearly wasn't setting company policy that day, I walked out, empty-handed.

Why did a cell-phone provider think it could demand my Social Security number? Because it can. There's no federal law preventing businesses from asking for it, and in most instances, no state law. The only recourse a consumer has is to walk.

IDENTITY THEFT • In 2001, the Social Security Administration received 65,000 allegations of the misuse of Social Security numbers. • In the first six months of 2002, the FTC received more than 70,000 complaints of identity theft.

The Social Security number, for those of us who have forgotten, is a government-issued identifier originally intended to track a worker's earnings, primarily for payment of one's federal retirement, survivor and disability benefits -- and, only later, for tax purposes.

But it's fallen prey to what consumer advocate Ed Mierzwinski of U.S. Public Interest Research Group calls "mission creep." Now one's Social Security number is often demanded by businesses for credit-checking, identification and record-keeping purposes. It's long been the number of choice used by health insurers, doctors' offices and schools. And some employers use it on company IDs.

Its widespread use is one of the top reasons identity theft has become what Mierzwinski, testifying before a Congressional committee, called "one of the nation's fastest growing white-collar crimes." You don't need to tell that to the more than 30,000 victims of what is potentially the biggest identity theft ring in U.S. history, for which three men were charged this week.

ID THEFT CHECK UP Click here to see if companies you deal with (or work for) are putting you at risk for ID theft.

Bottom line: be stingy with your personal information. With a name and a Social Security number, a thief can pose as you and, among other things, get a credit card, a cell phone, a bank account, a loan, a job, a utilities account or a driver's license -- and in the process ruin your credit and your finances.

There's only one circumstance in which Robert Ellis Smith, publisher of the monthly newsletter Privacy Journal, thinks consumers ought to give out their Social Security number: whenever an event might generate taxable income (opening a bank account, buying securities or a home, getting a job, etc.).

You'll never entirely erase your chances of falling prey to identity thieves. But you can lessen your vulnerability.

If merchants wants to run a credit check on you, ask that they do so without your Social Security number. Smith suggests politely trying this a few times, noting in his experience, some merchants have been willing to bend. "See if it goes through," he said. "If they say 'No,' go elsewhere."

The truth is, in most instances, a Social Security number is not required to pull up your credit report. "It's just one piece of identifying information," said Diane Terry, the director of the fraud victims assistance department at TransUnion, one of the three major credit bureaus. "If we can identify it without the Social Security number...we can release it that way."

A merchant can pull your credit report with just your name and address, she said. To insure they pull up the right report, give your full name with middle initial, your current address as well as any other addresses you may have had in the past five years.

Question a business about its security practices. The Federal Trade Commission, which runs an identity theft program, suggests you ask four things: why your Social Security number is needed, how it will be used, what law requires you to provide it and what will happen if you don't.

Never write your Social Security number on a personal check. Some stores may say they require it to accept your check. But "they don't need your Social Security number," said attorney Naomi Lefkovitz of the FTC. And if they're using it for identification purposes they can select some other way, she said, such as asking for your phone number or a photo ID.

USEFUL SITES • FTC's Cybertool for ID Theft Investigations • Privacy Rights Clearinghouse • Social Security Card Protection • When someone misuses your Social Security number • Privacy tips from "Privacy Journal"

Don't give it to a video rental store. Why some video stores request Social Security numbers is a mystery to Lefkovitz, Terry and Social Security Administration spokeswoman Carolyn Cheesum. Both Terry and Cheesum have refused to give their numbers in such a situation and suggest you do the same. The same goes for health clubs.

Ask for a new password or account number. Often, Lefkovitz said, businesses use your Social Security number as your ID number. Ask that they use a random number instead. This strategy worked for her when she applied for insurance. And don't give your mother's maiden name either, which companies often use as a password, she said.

Given the daily pressures in your life, it will always be tempting to give in to the wheezy clerks of the world. Being defiant takes time and energy.

But it won't take nearly as much time and energy as you'll need to re-establish your good name and credit should someone steal them.

And the more likely it is you'll effect change. If you opt to leave a store because a merchant insists on getting your number, "send a letter to corporate headquarters and say I'm not using your business for this reason," Lefkovitz recommends. "If everyone starts doing it, businesses will eventually respond."

Jeanne Sahadi writes about personal finance for CNN/Money.com. She also appears regularly on CNNfn's "Your Money," which airs weeknights at 7 p.m. For comments on this column or suggestions for future ones, please email her at everydaymoney@cnnmoney.com.