What it does: Sends you e-mail alerts when new accounts, inquiries, negative information, credit-limit changes, and other items appear on your credit report.

What it costs: If you buy direct from Equifax, you'll pay $12.95 a month. If your personal information has been compromised by a security breach, the company involved will often pay for monitoring for a limited time.

Should you do it? No. A security freeze should stop the opening of fraudulent new accounts, negating any need for ongoing monitoring. You can monitor suspicious activity on your existing credit and bank accounts—the ones a scammer is most likely to target—by signing up for online access and checking them daily or weekly.

Neither the FTC nor consumer groups, including the Identity Theft Resource Center, the Privacy Rights Clearinghouse, and Consumers Union, recommend or endorse credit-monitoring services.

Where to get it: All three credit bureaus sell this service, but Equifax is the cheapest.

Beware: Monitoring offers limited protection. It won't pick up "fragmented files" created by credit bureaus and kept separate from your files when your Social Security number is used with someone else's name and address. And it can take as long as 60 days for a fraudulent account to show up in your credit reports.

This article was also published in Consumer Reports Money Adviser. Subscribe now to get more expert financial advice you can trust.