But the deadline for signing up for free credit monitoring from Equifax is Jan. 31.

[Editor’s note: On Jan. 31, Equifax introduced Lock & Alert, a free service that lets those who are enrolled to lock and unlock their credit report, and be alerted each time it is unlocked.]

In September 2017, Equifax—one of the three major credit reporting companies in addition to Experian and TransUnion—revealed that hackers had breached its security and gained access to sensitive information about millions of customers.

Social Security numbers, names, dates of birth, and addressed of around 145.5 million customers were compromised in the breach. Some drivers license numbers were also accessed by the hackers, according to Equifax.

The hackers also stole the credit cards numbers of 200,000 people, who Equifax notified by mail. If you are still not sure if you were impacted by this breach, you can check here.

There are several ways to protect yourself if you think your data may have been stolen—credit score monitoring, credit locking, and watching your accounts for suspicious activity. Fortune has a helpful explainer about what to do, and the New York Times has a handy how-to guide for freezing your credit.

Freezing your credit report is one way to protect yourself from identity theft. It keeps lenders from accessing your credit score and thereby prevents lenders from issuing new credit in your name. Freezing your score won’t interfere with existing business relationships you already have with credit card companies and banks. But it does mean that nobody new including potential employers and landlords can get access.

For the record: Freezing your credit does not hurt your credit score.

Correction: An earlier version of this article mistakenly said that the deadline for freezing and unfreezing credit reports for free was Jan. 31. In fact, it is June 30. The headline has been updated to reflect the change.