Placing a freeze on your credit report is one of the initial steps you should take if you discover you are the victim of identity theft. This temporary freeze prevents the information in your credit file from being reported to companies, credit grantors etc. The short version is that nobody can run a credit inquiry and see your credit report. This prevents further fraudulent accounts from being opened with your social security number and personal identifiable information.
Only the individual who’s social security number is attached to that credit file can request a temporary credit freeze or a temporary lift of the credit freeze. Keep in mind that you will not be able to apply for new lines of credit, loans or mortgages while the freeze is in place, so you will need to plan ahead if you know that a creditor may need to pull your credit report in the near future.
When submitting for a credit report freeze, you must do so with ALL 3 CREDIT BUREAUS. Equifax, Experian & TransUnion. Additionally, if you wish to temporarily remove the freeze, you must again request the lift with all 3 bureaus. After you freeze your credit files, it will be necessary to monitor your credit reports over the next several weeks & months, to ensure no new fraudulent accounts were reported before you set the security freeze.
via SIF.org http://www.stopidentityfraud.org/2016/03/30/how-to-freeze-your-credit-report/