COLUMBIA — Experian is notifying South Carolina parents they can begin signing up to have their children’s credit monitored, Gov. Nikki Haley announced Friday.

The Family Secure service is part of the state’s response to the hacking of millions of taxpayers’ personal data. The theft, first announced Oct. 26, compromised nearly 4 million individual tax filers, including the unencrypted Social Security numbers of 1.9 million dependents on parents’ tax returns.

Experian began sending emails and letters Thursday on the availability of Family Secure, free to parents for one year after sign-up. The cost is covered by the state’s $12 million contract with the credit bureau.

Most children under 18 don’t have a credit history, particularly pre-teens. The parent who signs up will be alerted if a credit file pops up in a child’s name. If a file exists, the service will monitor for suspicious activity.

“If you claim minors as dependents, you should absolutely take the time to sign them up for identity and credit monitoring through Experian’s Family Secure,” Haley said.

A parent must first enroll in Experian’s ProtectMyID service, which provides a year of credit monitoring for each adult signing up. Its availability was part of the initial Oct. 26 announcement on the breach.

Notification began going out to parents already enrolled in ProtectMyID. As of Friday, more than 900,000 South Carolina taxpayers had signed up, said Experian spokesman Greg Young.

Experian will stagger the notices over the next several weeks. Parents and legal guardians have until May 31 to enroll in Family Secure. Parents can sign up any child under 18 who is claimed as a dependent on their tax returns.

The deadline for signing up for ProtectMyID is Jan. 31.

Haley specified last week that the hacker took data from 3.8 million individual filers and 700,000 businesses. Beyond unencrypted Social Security numbers, data stolen included 3.3 million unencrypted bank account numbers and 5,000 credit card numbers now expired.