Placing a security freeze on a credit report restricts new lenders to view your credit report and screens you from preapproved credit offers as well. However, in most of the cases your existing lenders will be an exception to this rule. Your existing creditors with whom you already have running accounts will be able to use your credit history for the purposes of reviewing and updating your portfolio. This also means that any credit card that needs to be reissued will go through without any problem.
Other exceptions are gaining access to your credit report for the purpose of preventing fraud, by using a credit monitoring service to which you have subscribed and for law enforcement purposes as well.
In order to find a complete list of who VIEW your credit report and under what circumstances check with your state laws.