Target is apologizing to its customers in full-page ads in several major newspapers Monday over its recent security breach. (Reuters)

Target said Monday that its customers may now sign up for a free year of credit monitoring and identity theft protection, as part of its response to a massive data breach that may have leaked information on at least 100 million customers.

To sign up, customers are asked to go to a Target Web site and enter their e-mail address to receive an activation code; Target said the e-mail address entered at this site will only be used to send the code and not for any other purpose.

Target spokeswoman Molly Snyder said that customers have signed up quickly for the free services. “As soon as the site went live we had an immediate, strong response to the offer,” she said in a statement.

Anyone who has shopped at Target may sign up for the service. If you share a credit or debit card used at Target store with another person, both of you may sign up for the credit monitoring, according to a set of frequently asked questions posted on Target’s corporate Web site.

Shoppers have until April 23 to register for their activation code. All codes must be redeemed by April 30.

Target partnered with credit card monitoring firm Experian to handle the monitoring for its customers. Once users get their activation codes they’ll be asked to enter a variety personal information into the Experian Web site to verify their identities for the credit monitoring. This includes information such as address, social security number and mother’s maiden name — all to ensure that consumers get the right credit reports. Target will not have access to the data.

Once users are signed up for the service, they will receive a complimentary copy of their credit report and the option to receive daily credit monitoring, access to fraud resolution services and identity theft insurance where available.

The services are all part of Experian’s “ProtectMyID” package and are free for 12 months from the day of enrollment.

ProtectMyID does not include credit scores from Experian or other credit monitoring bureaus. Users may elect to purchase that service separately but are not required to buy a credit score report to use the ProtectMyID service.

Users will not automatically be re-enrolled — or charged — when the free service stops.