Nearly half of Americans may have had their information stolen in the massive Equifax data breach revealed last week, and experts say freezing your credit is one line of defense. The credit-reporting company said hackers stole personal data — including Social Security numbers, names, addresses and dates of birth — from an estimated 143 million Americans.

Here's how to know if you should freeze your credit, with steps on how to initiate a freeze if you decide to do so.

Protect yourself: How to defend yourself against identity theft after the Equifax data breach

More on the breach: Equifax's struggle after massive security breach deepens

What is a credit freeze?

A credit freeze prevents creditors from accessing your credit report, according to the Federal Trade Commission. It prevents credit, loans and services from being approved in your name without your consent. It does not affect your credit score. 

If I freeze my account, are there still some people who can see my credit report?

Yes. 

  • You can see it. You're still entitled to your free annual credit report.
  • Your existing creditors and debt collectors acting on their behalf can see it. 
  • Government agencies may have access to it (think, subpoena or search warrant).

But what if I want to lease a car or rent an apartment?

If you institute a freeze and a creditor needs to access your credit report, you'll need to temporarily lift it. When you initiate a freeze with each of the credit reporting companies — you have to do freezes with all of them — you'll get a pin that corresponds with each freeze. When you want to temporarily lift any of them, you'll give that pin back to the credit reporting company it corresponds to. If you're trying to lease a car at Toyota, for example, you can ask Toyota which credit reporting company they're going to use to access your report. That way you can just lift the freeze at that company.

How long does it take to lift a freeze?

No more than three business days, according to the Federal Trade Commission.

But what about when The Gap says I can save 10% on my purchase if I open a new credit card? Won't it need to access my credit report right away?

Yes. With a freeze in place, you won't be able to take advantage of those on-the-spot offers. 

Does a credit freeze cost money?

Yes. Fees vary from state to state, and range from about $5 to $10. There are also fees to lift the freeze. You can see fees by state here. Equifax, however, has currently waived fees for initiating a credit freeze. 

How do you determine if you were exposed in the Equifax breach?

Visit Equifax’s website, www.equifaxsecurity2017.com, and click on the tab that says "Potential Impact." You'll be asked to enter your last name and the last six digits of your Social Security number. You'll either get a message that says "we believe that your personal information was not impacted by this incident" or "we believe that your personal information may have been impacted by this incident." 

How should I decide whether to freeze my credit?

Freezing your credit — as well as lifting a freeze — may be a bit of a headache (everytime someone wants to access your credit report, you'll have to go through the process of lifting the freeze), but it will protect you against some identity theft crimes. Even if you escaped Equifax's breach, you've probably been a victim of a previous one. 

"You never know for sure 100%, but you should assume your data has been compromised either in this breach or in previous breaches," said Avivah Litan, a security analyst at financial research firm Gartner. "Well over half the population has been breached even before this. There's a greater than 50% chance that you have been compromised. That's what you should assume, no matter who tells you what." 

Where do I begin?

To place a freeze on your credit reports, you need to call the credit reporting companies. There are three big ones — Equifax, Experian and TransUnion — and one smaller one, Innovis. Litan recommends freezing your credit at all four. Here are the numbers to call:

  • Equifax — 1-800-349-9960 
  • Experian — 1‑888‑397‑3742
  • TransUnion — 1-888-909-8872
  • Innovis — 1-800-540-2505

Additional information on credit freezes:

What kind of information will I be asked to provide?

Personal information, including your name, address, date of birth and Social Security number. 

Can I initiate a credit freeze online?

You can, but Litan says you shouldn't. Picking up the phone is far less risky.

"The bad guys are going to use this as an opportunity to scam consumers further," she said.

I've been offered the option of locking my account vs. freezing it. Is that something I should consider?

Litan says no: "It looks comparable, but it's too vague." Ask explicitly for a credit freeze, she said.

Contributing: Adam Shell