You no longer have to pay to freeze or unfreeze your credit reports under a new federal rule.

A credit freeze is an extremely effective way to prevent identity thieves who get their hands on your Social Security number from obtaining loans or credit cards in your name. The freeze blocks credit bureaus from sharing your credit reports with lenders, and lenders won’t open new accounts when they cannot access these reports.

Previously, consumers typically had to pay $3 to $10 to each of the three major credit bureaus—Equifax, Experian and TransUnion—to freeze or “thaw” their credit reports. These fees could add up for consumers who frequently thawed their credit reports to apply for loans or credit cards and then refroze them, incurring a new round of fees each time. (Freeze fees have varied by state, and free freezes already were available to certain people, including identity-theft victims.)

The new rule that makes credit freezes free comes about a year after a security breach at Equifax exposed the personal data of 143 million people to hackers. After the breach, Equifax began offering its freezes for free and is extending that offer until the new rule affecting all the credit bureaus takes effect.

What to do: Freeze your credit reports at each of the three credit bureaus even if you already pay for a credit-monitoring service from one or more of the bureaus.

Reason: Credit monitoring can only tell you that an identity thief has opened or tried to open an account in your name—it can’t prevent that from happening. A freeze can.

After you freeze your credit reports, you will have to thaw them before applying for credit (and refreeze them again later). Instructions for doing this can be found on each bureau’s website.