Stop whatever you’re doing (except reading, that is) and listen up. If you’re a human being with an identity that you prefer to maintain sole control over, consider the following piece of advice: Place a security freeze on your credit reports.

Setting up a security freeze means putting your files on hold at credit bureaus. Doing so will prevent anyone who has amassed enough information about you from opening up a new line of credit in your name. This is the surest way to prevent a criminal from spoofing your identity and suckering banks or credit card companies into approving new, unauthorized accounts in your guise.

Whom should you call? There are three major credit reporting agencies: Equifax (EFX), Experian (EXPN), and TransUnion (TRU). Phone each of them. They will walk you through the process.

Go, do it. Done? OK, good. Don’t worry, you can always “thaw” your account later. Credit bureaus are legally bound to lift freezes within three days.

Such is the advice of the U.S. Public Interest Research Group, a federation of nonprofits that acts as a consumer advocacy group. The organization recently published a report—“Why You Should Get Security Freezes Before Your Information Is Stolen”—that outlines this tip in detail. As the paper explains:

Most creditors will not issue new credit to a customer if they cannot see that customer’s credit report or score derived from it from at least one of the three major national credit bureaus. So if a thief applies for a new account in your name with your Social Security number and his or her own address, but your credit report is frozen, creditors will simply not open a new account.

It’s a simple preventative tactic. There is, however, a stipulation: Freeze and unfreeze requests are not always free. They can cost up to $10 or $12 depending on your state of residence or age. It depends. (Determine your qualifications by dipping into the report.)

Now let’s address credit monitoring services. Often when a company gets hacked—releasing its customers’ personal information into the digital wilds for hackers and crooks to exploit—that company will offer the victims credit monitoring at no cost for at least a year or two. This minor consolation is really nothing more than a face-saving maneuver, as the authors of the report explain. Monitoring only detects fraud after the fact—and besides, you can run the checks yourself. From the U.S. PIRG report:

Paid credit monitoring services in particular are not necessary because federal law requires each of the three major credit bureaus to provide a free credit report every year to all customers who request one. You can use those free reports as a form of do-it-yourself credit monitoring.

Thanks for nothing, breached companies. So be proactive, dear reader. Use protection. Freeze your credit files.

H/T Brian Krebs at Krebs on Security, who has advocated on behalf of this advice for a long time.

Follow Robert Hackett on Twitter at @rhhackett. Read his cybersecurity, technology, and business coverage here. And subscribe to Data Sheet, Fortune’s daily newsletter on the business of technology, where he writes a weekly column.

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