https://consumerist.com/2017/09/21/is-experian-letting-anyone-access-your-credit-freeze-pin/

Placing a credit freeze on your accounts following a hack or issue with identity theft is only effective if the credit reporting agency you’re working with doesn’t give ne’er-do-wells the ability to unfreeze the accounts by providing the same information that any good ID thief already knows about you. This is a lesson some victims of Equifax’s recent data breach are learning after freezing their accounts with fellow credit reporting agency Experian. 

Krebs On Security reports that a possible security flaw in Experian’s credit freeze process could leave victims of Equifax’s breach open to further fraud.