https://www.theregister.co.uk/2018/10/10/experian_credit_pins/

Experian's website exposed to world-plus-dog the PINs needed to unlock frozen accounts, allowing crooks to potentially apply for loans and credit cards as their victims.

The credit-monitor agency lets people freeze their account using a PIN that has to be submitted in when applying for stuff like loans: it's a mechanism that's supposed to stop fraudsters from exploiting stolen personal information, such as names and social security numbers, to obtain credit using someone else's identity.