Updated on October 9, 2007.

CALL IT POST-TRAUMATIC STRESS: For victims of identity theft there's always that nagging feeling that once a thief's been able to open fraudulent accounts in your name, it's just matter of time until they do it again.

Now states are enacting laws that offer consumers the ultimate protection: a credit freeze. It basically allows you to have the credit bureaus lock up your file and with it, the ability to get any type of new credit. Whenever someone applies for a credit card or loan in your name, the lender is unable to access your credit score and report, and the application is denied. To date, 39 states plus the District of Columbia have passed some sort of credit-freeze legislation.

Consumer advocates, who have been lobbying for credit freezes for more than 10 years, say that's the only guaranteed way to prevent identity theft. But the credit bureaus counter that a credit freeze creates inconveniences that, for most people, may not justify the benefit.

"While there might be some consumers for whom it might be the right solution, for many there are other remedies to prevent identity theft before pursuing the extreme measure of putting a freeze on your file," says David Rubinger, a spokesman for Equifax, one of the three major credit bureaus.

Granted, the credit bureaus have a vested interest in discouraging credit lock-ups: After all, they're in the business of selling them to creditors. "They don't like the freezes because they give consumers control over their credit information," says Ed Mierzwinski, Consumer Program Director of the U.S. Public Interest Research Group, or U.S. PIRG. In addition to that, Mierzwinski says, should credit freezes become the norm, the sales of credit monitoring products a lucrative and growing part of the industry's business is likely to decline.

Freezing one's credit can be a hassle for consumers as well as credit bureaus. Once it's in place, consumers themselves can't legitimately apply for credit without asking the bureaus to "thaw," or remove, the freeze. Because this takes up to several business days, it can prevent people from getting "impulse" credit, for example, by applying for store credit cards to receive discounts. "You have to be organized and know when you're going to apply for credit," says Mari Frank, an attorney in Laguna Niguel, Calif., and the author of two books on identity theft. "If you're in need of cash quickly and you want to apply for a credit card, you won't be able to do it. But if you plan ahead, you can feel more comfortable and safer."

Here's what you need to know about credit freezes.

Who is eligible?
For details, check the Consumer Union's database

Who is eligible? That depends on where you live. Currently, 34 states allow anyone to freeze their credit file, whether they've been a victim of identity theft or not, says Susanna Montezemolo, a policy analyst with Consumers Union, an advocacy group. Four states Arkansas, Kansas, Mississippi, and South Dakota only make credit freezes possible for identity-theft victims who typically have to present some proof, such as a police report. And beginning in September 2008, the security freeze law in Washington will apply to all consumers not just identity-theft victims. A bill introduced in Congress aims to make the security freeze a federal law that applies to all consumers.

Weighing the consequences
Most states that have freezes mandate that the bureaus unfreeze the file on the consumer's request within three or five business days. However, according to Frank, in reality the job may take longer. "These are big companies, you know how it works," she says.

The good news: State legislators are listening to consumer advocates' pleas for more flexibility and a number of states, including Tennessee, Utah, Washington and Wyoming, and the District of Columbia, will require the bureaus to unfreeze files within 15 minutes by September 2008. Laws passed in Delaware, Maryland, Montana, and Nebraska will go into effect by January 31, 2009.

Typically, victims of identity theft can freeze their files for free. For details on each state's regulations, click here

With an increasing number of employers and landlords reviewing applicants' credit reports, a security freeze could also affect your job or apartment search. However, there are exceptions: Fourteen states permit landlords and employers to pull your credit report even if it's frozen, according to the Consumers Union. (For details, see our table.) Two more states Nevada and Wisconsin also allow employers to overwrite a freeze.

Don't let your guard down
As effective as it is, a credit freeze isn't a panacea for identity theft. For example, it won't protect you against check fraud, Frank notes. It also doesn't protect you against existing-accounts fraud, which happens when someone fraudulently uses your existing credit card or drains your bank accounts. Last year, the majority of identity theft (72% of all cases) took the form of existing accounts fraud, according to Javelin Strategy & Research's 2007 Identity Fraud Survey. That includes fraud using existing credit or debit cards, as well as checking and savings accounts, existing loans, insurance, telephone and utility accounts.

To protect yourself, be sure to review your credit card and bank statements regularly. You're also eligible for one free copy of your credit report from each credit bureau each year. To get yours, go to annualcreditreport.com.