NEW YORK -- Credit Karma, a free credit education website, this week added credit monitoring to the list of services it offers to its registered users.

The deal: has offered free credit scores for a few years, and has now added free credit monitoring.

The service tracks credit reports provided by credit reporting agency TransUnion. That means if TransUnion gets a request for information regarding a new credit application or adds a negative item such as a late payment to a credit report, Credit Karma will send an email letting the individual know, said founder Kenneth Lin.

The service is available to the site's 4 million existing users, in addition to new users as they sign up. Everyone must opt-in by providing details such as their Social Security number and birth date to enable the service to track credit history. Lin said the site does not share personal information. It uses several well-known security measures to protect users' data.

The benefit: Everyone is entitled to one free credit report per year from TransUnion, along with one from both of its two major competitors, Equifax and Experian, each year through www.annual .

What Credit Karma is offering is a service that many banks and others typically charge around $12.95 a month, marketed as identity theft protection -- a program that provides a heads up when there is activity related to your report.

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Although Credit Karma's service does not include information from the other two agencies, which many ID theft monitors do, it still provides a good way to keep tabs on what's happening with your credit. It can give you a heads up if your identity is stolen or if someone is applying for cards or accounts in your name.

The downside: Credit Karma provides credit scores produced by TransUnion and VantageScore, but does not offer FICO scores, which are the most widely used among lenders. The scores it provides can give you a good idea of where your credit rating stands, but may not match up with the scores your bank uses if you apply for a loan or credit card.

The fine print: Credit Karma earns its revenue through advertising that appears on the site. Lin said the ads may be targeted to users based on the information they provide.

For instance, users with very high credit scores may see ads for cash-back credit cards that are marketed to consumers with strong credit histories.